This guide will teach you the basics of what alt text is, why it’s important, and how to write it. The example images used are specific to book historians to help you write alt text for your course materials, your books or articles, and other presentations. You can also download this as a Word file.
If you notice an error in any of the descriptions, see an image that shouldn’t be published here, have any suggestions for additions to the guide, or have any questions, please contact the SHARP News admins or the author of the guide: Ellen Forget ellen.michelle@mail.utoronto.ca.
The copyright for all images in this guide remains with the original copyright holders.
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What is alt text?
The term alt text is short for alternative text. Alt text is an important accessibility tool for visual elements of digital content so people who use or rely on screen readers can understand images or videos. Alt text should describe the visual stimuli accurately but concisely, and it should be free from bias and undue interpretation.
Alt text is not the same as a caption. A caption provides contextual information related to the image that assumes the reader is aware of the content of the image. The alt text provides a description of the image to those who cannot see the image clearly or are listening to the document using a screen reader. Not every image needs a caption, but every meaningful image needs alt text.
The only images that do not require alt text are images that are purely decorative. These images must not hold significant meaning to the rest of the content in the document. The document should be fully understandable and considered complete whether the image is there or not. If that is true, then the image is decorative and does not require alt text.
Length of alt text
Alt text fields typically allow up to 1,000 characters. However, this does not represent the average desired length of alt text. The required length depends on the complexity of the image and the level of detail being shared. Some images may only need a few words and other images may require a couple sentences. Alt text should be descriptive, but concise. It should describe the important aspects and details of an image, while details that are unnecessary or superfluous to the intended meaning of the image can be omitted.
In some cases, to provide meaningful alt text of an image or a data visualization could require a greater character count than is allowed or preferred in the alt text field. For such images, it is recommended that you use short alt text and long alt text. In this case, the short alt text would include a very short description of the image and a note that further details are available in the long alt text. Then, in the back matter or appendix at the end of your document, you can include a section for long alt text. The benefit of this method is that readers can decide for themselves if the context of the surrounding text plus the short alt text is enough for them to understand the image or if they want or need the further information available in the long alt text. This can be especially useful for data visualizations to include accessible tables of data in the long alt text compared to the visual charts or graphs available in the main text.
The importance of context
Context plays many roles in considering how to write alt text. Images are usually not isolated. If you are including images in an academic article, the main text in the article can help explain the image. If there is detailed discussion of the image in the main text to provide context for that image, your alt text might be shorter because the details are already described. You must also consider who the audience is for your publication and write alt text in the language they will understand. For example, if you have an image of a medieval manuscript, how you describe that image may change if your document is meant for undergraduate students who are beginning to learn about such manuscripts or if your document is meant for experienced archivists and librarians. For the former, you want to avoid the use of jargon that would be appropriate to use for the latter audience. The goal is to ensure the intended audience of the document can fully understand the alt text, in the same way that you would ensure your main text is understandable.
Text-based images
There are many circumstances that may lead to images with a lot of text. In particular, there may be a lot of text on a magazine cover, on a slide in a presentation, or on images of book interiors. There are two pieces of best practice that should be considered when working with text-heavy images: 1. Be concise and include only the information required to understand the image, and 2. Include the text in your alt text so screen reader users have the same information as those looking at the image. There is a delicate balance between these two recommendations when dealing with images that have a lot of text, and context is important. If you’re showing the image because of the text it contains, then that text should be included in the alt text. If you’re showing the image for reasons other than the text, then describe the important pieces and either leave the text out or include it in long alt text.
Type of image
There is no need to start your alt text with “picture of” because the screen reader will indicate to the listener that it is alt text for an image. The only time you may want to start your alt text with a description of the format is if that format is particularly unique. If you have a document full of images that are photographs and you have one that is a drawing, then you may want to start with “drawing of” to indicate the form. However, if every image is a drawing, then that can be indicated in the main text and then avoid including it in your alt text.
Automatic alt text generators
As awareness of accessibility and alt text increases, tools have been created to automatically generate alt text for images and videos. These tools can be incredibly useful as a starting point for writing your alt text, but I strongly recommend that you review and edit the alt text, or simply write the alt text yourself. These automatic image description generators can misinterpret parts of the image, misunderstand which parts of the image are important and which aren’t, misunderstand the context of the image, and just simply get things wrong.
Alt text examples
Book and magazine covers
We’ve all heard the phrase “don’t judge a book by its cover;” however, people do judge books by their covers. The cover of a book can tell the reader a lot about what to expect from that book. The cover can show the book’s subject matter, genre, and tone, and perhaps even the intended age group. If a book’s cover can do all that work for a sighted reader, the alt text needs to do that for a visually impaired reader as well. You must choose which details are important to get that information across, and which details are superfluous. For example, you typically won’t have to describe the specific font used on the cover, but you may want to if you’re describing a graphic design book or a horror novel that uses a specific horror-genre font (particularly if the rest of the cover is vague regarding genre). As much as possible, all text on the cover should be included in the alt text. The title and author are important, but so are any accolades or blurbs on the cover, as they are designed to help sell the book. In the case of magazines, as in two of the examples below, the text on a cover is also used to help sell that issue of a magazine and should be included when possible; however, there is often more text on a magazine cover than a book cover, and that can sometimes make the alt text too long. In that case, either summarize the text, include only top-level highlights, or make use of the long alt text feature to include all of the text.
Alt text: Cover for Women’s Art Magazine, a women artists slide library publication. No 50 published in January/February 1993. The price listed is £2.50. The cover features an anthropomorphized painted portrait of an orange cat in a light green suit. Text along the bottom reads: “Angelica Kauffman, Faces: Fair to Fake, Paula Rego, Berthe Morisot.”
Alt text: Cover of Make: The Magazine of Women’s Art. The cover features a photograph of a woman with dark hair wearing traditional Indian face jewellery on her forehead and nose, and her face is painted with the Union Jack flag. The text describing the contents of the issue read: geographies, nationalisms/localisms, a sense of place. Featured articles include: from Edinburgh to Riga, Poles apart, inner maps, waving not drowning, Marion Kalmus, Kerry Stewart, and Mella Jaarsma in chicken skins.
Alt text: Book cover for Graphic Design by Matthew Baranski. The cover shows the words “graphic design” in all caps in sans serif font five times alternating colours between light grey on dark blue background and yellow on grey background.
Book interiors
The interior pages of books will often have a lot of text, which can make the alt text too long. When using images of book interiors, you have to determine what part of the image is important. What is the reason you are using this image? If it is for the text itself, then include the important parts of the text. If you are showing the image for other reasons, such as showing markings on the page, then you can omit the text or include it in long alt text.
Alt text: Title page spread of The Principles of Archive Repair by Roger Ellis. The verso page has three markings made with blue crayon and the recto page, with the title page text on it, has one similar marking that does not obscure the printed text.
Images with non-primary language text
When coding text, it is possible to add a language tag to text that appears in languages other than the primary language of the text so that screen readers pronounce those words appropriately. However, it is not possible to add language tags inside an alt text tag. Therefore, it is the best practice recommendation that text in an alt text description should be translated to the primary language of the document with a note that describes what language the text appears in on the image. If you have many images with languages other than the primary language of the document, it is recommended to put the exact text in its original language in the main body of your text (or in long alt text) with a language tag so that content is available to all readers. However, context is important. If the text itself on the image is not an important part of the image or the reason for including the image in your document, then it may not be necessary to include it in full. Consider your audience and the context of the image.
Alt text: Greek book cover for Franz Kafka’s Metamorphosis. The cover image features a large cockroach with a small silhouette of a man in a suit standing within the image of the bug. The title and author name appear in Greek on the cover.
Data visualizations
Complex images, such as data visualizations, can be difficult to describe concisely. Charts, graphs, and maps can contain a lot of detailed information. As always, context is important. Consider which details are important to the reader and the reason for including these images in your document to determine how to describe it. In some cases, exact, detailed information is required, and you should consider including both short alt text and long alt text. The short alt text would provide a summary of the image and it would then link to the long alt text at the end of the document, which would provide a more detailed and exact description of the image. This method ensures that readers can choose whether the summary is enough for their understanding or if they require the longer description. You may also consider using a screen-reader-friendly table of data in the long alt text for overly detailed data instead of describing it in prose.
This chart could be converted to a table in the long alt text for screen-readers with format and the publication year as the axis headings and the value as the content inside the table. With a chart like this, there may be multiple lines with the same publication year and format, so you could present the average values or have one line per book, depending on the context of the data and its importance to understanding the main text.
Some simpler data visualizations, like this bar graph, can be described entirely in the alt text. The sample alt text below describes the content of the bar graph in numerical order, rather than in the order presented on the image. This is often recommended so the reader knows the value-order immediately without having to remember the individual numbers presented. However, in some cases it wouldn’t be appropriate to alter the order, particularly if the chart uses chronological order and that order is important to understanding the context.
Alt text: A chart describing the average price in reales by book format. Folio is valued at 7.11 reales, 12mo is valued at 4.26 reales, quarto is valued at 3.61 reales, 16mo is valued at 2.83 reales, octavo is valued at 2.71 reales, 32mo is valued at 2 reales, 24mo is valued at 1.54 reales, and format unknown is valued at 0.49 reales.
PowerPoint slides
If you create slides for your classes or conference presentations and post them to a website for people to access, it may be useful to write alt text for each slide to post with the slides. The complexity of alt text for slides depends on the complexity of your slides. Simple slides with just text are easy: just write out the text on the slide as the alt text. For more complex slides with images or data visualizations, consult the alt text examples for those types of images and ensure that the important parts of each slide are described in your alt text. If you include multiple images, such as a collage, on one slide, consider which images are the most important for the reader to understand the purpose and intent of the slide.
If the image is mostly illustrative and the content of it is not important to the overall meaning of the slide, then your alt text might look like this.
Alt text: The slide title is “Functions of Publishing” and the text reads: “Frames: ‘distribution mechanisms, channels and media … contexts, modes of understanding’ p.84.” There is a screenshot of a Wattpad web page.
However, if the content of the image is the most important piece of the slide, then your alt text might look like this.
Alt text: The slide title is “Functions of Publishing.” There is a screenshot of a Wattpad web page that discusses why authors should consider publishing on Wattpad, claiming that “your original story could be the next big hit” and “your voice belongs on bookshelves.” The page can be found at: *insert link to webpage*. Text on the slide reads: “Frames: ‘distribution mechanisms, channels and media … contexts, modes of understanding’ p.84.”
If you have a video recording of the slide presentation and you read that quote out during the presentation, then you might not need to include the quote in the alt text as well. (Just be sure you also have a transcript of your recording available for further accessibility.)
Conference images
Many conference organizers and attendees like to post pictures on social media from the conference they’re attending. This is a great way to encourage accessibility, as some people who were unable to attend the conference may follow along with it on social media. Most social media sites will allow you to add alt text to the images you share. (If you aren’t sure how to add alt text to your social media images, check out the Accessible Social website for instructions.) There are many different types of pictures you might take at a conference. These examples might not cover everything, but they should hopefully get you started. As with many of the other examples in this guide, context is important and you should always think about what the important parts of the image are.
Alt text: A panel presentation at the SHARP 2022 conference. There are three presenters on the stage, and the audience is pictured from behind.
This first example keeps it simple, which would be perfect for a quick social media post. You could even leave out the bit about the audience if that’s unimportant. If you know the names of the presenters, that could be useful to include as well. There are also more details you could include, depending what the purpose of this image is. Perhaps you want to include a note that “approximately 15 people are pictured in the audience” or if the particular room this panel is happening in is important for context, you could say “A panel presentation in the X Room at Y building/venue.”
Alt text: The opening keynote presentation by Kathryn Rudy at the SHARP 2022 conference. The slide shows a spread of a medieval manuscript with a decorative image on the verso and text on the recto. The citation for the spread reads: “Brussels, Royal Library IV 1095, fol. 27v-28r.”
Again, this example is assuming a general audience with only a basic need to understand the contents of the image. If the slide visible in the image is the most important thing in the context of you sharing this image, then you may want to go into more detail about the spread being shown, but also if the citation on the slide is present in the main text, then you can omit it from the alt text. If the room is important, then you may wish to describe the chandelier or the architecture of the room.
Images without an object of focus
Sometimes you may have general images that show a whole room or a large area or group of objects that does not include one main focus. These images tend to have a lot of small details that may be noticeable to a viewer, but aren’t necessarily important to the image or the context of the image. In these cases, short, concise alt text is best.
Alt text: Rows of library shelves filled with books.
Alt text: A long hallway with library stacks filled with books on either side.
In this particular case, if the specific collection or topic section of the books is important, you can include that information as well.
Book art images
The examples given here of book art images are more complex than simple book covers or book interiors, because there is additional context of these images that they are art installations as well as books. The important part of the image might not be the books themselves, but how they are arranged or altered to create art. The examples here have simple alt text. The assumption is that if the specific details of the art are important to the main text, those details will be explained in the main text as well as being shown in the image. If those details are described in the main text, then they do not also need to appear in the alt text.
Alt text: An art installation created with eight open books in two columns. There is a tear in the middle of each book running down the centre of the columns. There is text added to the spreads on the top six books that reads “the wifi is weak” in all capital letters.
Alt text: A person lies on the ground with their arms outstretched and a book open on top of their face. Surrounding them are rows of books lying spine-up over A-shaped frames.
Special topics images
As a book historian or bibliographer, you likely have specialized knowledge of a particular subfield. Perhaps you specialize in medieval manuscripts, French poetry, or art history. Every specialty will have jargon that is specific to that specialty that people in other (sub)fields may not know or understand. When you are writing alt text for images that contain features with specific jargon labels, you may need to write multiple versions of your alt text for different audiences. If you’re using that image in a journal article aimed at a specialty audience, you can use jargon in your alt text and assume it will be understood; however, if you are using the same image in an undergraduate class or for a publicly viewable digital exhibit, you do not want to use specialty jargon that may not be understood by that audience.
We’re still looking for example images for sample alt text to show the difference between these two types of alt text. If you have an image you think would be helpful, please contact the SHARP News admins or Ellen Forget.
Additional resources
“A guide to writing alt text and accessible image captions”
