Writing short and concise alternative text is something of an art, as the information needed from each image is not always the same. This page goes over some general guidelines of how to write image descriptions. Go back to How to Write Alt-text for more documentation, or check out Samples of Alt-text.
Alt-text is read as a single line of text within the figure or image tags of an EPUB. Because of this there can be no complex formatting, including even paragraph breaks. This means it is very important to be strict with your punctuation. Punctuation will help create pauses for the screenreader.
There used to be a rule that Alt-text had to be 120 characters long, but this is no longer the case. You need to still aim to be as direct and concise as possible to avoid cognitive overload. This means that most Alt-text only needs to be 2-6 sentences long. Remember that it will be read all at once, which is why we have to be so careful with how we write it. Editing will become your friend. For more information, go to the section on Editing Alt-text. A good general rule is if the image requires more than 5 sentences for a description, or would benefit from the use of multiple modalities (i.e. tables or lists), then you can create a Complex Description.
Cognitive Loadis how much information they can store in their working memory. The average person can remember 5-7 items at one time. More than this can lead to cognitive overload. When writing Alt-text you need to aim for clarity and precision to avoid this. You can also learn more on how to do this in the Editing section.
General guidelines for writing are as follows:
Context is so important. Context is key! You must write all your descriptions based on the context in which the image is presented. The reading level, audience, surrounding text, and related images will all influence the description you are writing. The same image in a textbook that appears in a novel will have a completely different image description.
Before you start writing your Alt-text you must identify:
Surrounding text is any text that is around the image include:
Yes, you have to read the surrounding text before you write your image description. This will have the most influence on how much you describe or do not describe. Sometimes you might have to go further than just the surrounding paragraphs, so scanning a book section can sometimes be essential to your work. After you have read the surround text ask yourself:
This all influences how you describe the image. If an image is described in the surrounding text, you don’t need to repeat what is already described. Simply add anything that is missing, or be very brief with your image description. It is important to avoid redundancy.
The audience is the reader of the book. A textbook would have a different audience than a fantasy novel. Textbook readers can expect more technical terminology, whereas readers of fiction would expect more narrative language. Remember to always match the tone of the book.
If the image is repeated, you can shorten the image description depending on the context. If the image is in a sequence, or goes over 2 pages, go to Images Over 2 Pages and Images In a Sequence for more information.
Always write descriptions with a clear structure. Think of it as walking the reader through the image. It needs to be in a logical order for them to understand what is happening in the description.
Work from general to specific. Remember, the reader should be able to understand the description in one reading. This also helps avoid cognitive overload.
When writing Alt-text, your first sentence should sum up the whole image and work on its own as a description. Each sentence after that simply adds additional information that increases in detail as you write (i.e. General to Specific.) Think about the components of the image, and organize them from most important to least important. A good image description should walk the reader through the image in a logical and clear way. Most image descriptions should do the following:
Alt text: An outdoor garden on a sunny day. The garden overlooks a forested valley. The garden is made up of five raised beds, about 3 feet by 5 feet each. Nothing appears to be planted, but one of the garden beds is sprinkled with mulch. To the left of the beds, there is a wooden bench. At the bottom of the picture, a coiled hose is partially visible.
If you removed the end sentence, it would still be a complete image description. In fact, the first sentence can be enough for an image description. This is a great example of how to go from the general to the specific in an order that makes sense to the reader. You want to walk the reader through the description and avoid any confusion.
Use plain, simple, direct language and be precise. The description should be accessible to any reading level. For example, if you are describing a leafy tree do not use the word deciduous as it is too complex, be simple and direct and use green leafy tree.
Always be culturally aware and sensitive to what you are describing. You may need to do some research to find the right words to describe a piece of clothing, or a part of a diagram, but using the right terminology will not only help you be more concise, it will also ensure you are being respectful.
Avoid phrases like “image of”, “table of”, etc.. The screenreader will already pick up that it is an image or table, so writing this will be repetitive and redundant.
You can mention the type of image if it fits the context of the book. If you have a book that is all black and white images, or another specific yet consistent style, you only need to provide this information in the first image description–don’t repeat it in the following images.
For example, the first image’s Alt-text would read: "A black and white photograph of a teenage Asian girl looking out a window on a train." All following images will only have the image description without the phrase "A black and white photograph" (i.e. "The teenage Asian girl stands on the platform of a train station with her luggage on the ground beside her. She waves with a smile on her face.").
If the style changes in the book, for example all the images where photographs and then there is a newspaper clipping, state at the beginning of the image description for the newspaper clipping what it is: “A newspaper clipping with a headline that reads: “…”” For the photograph that directly precedes the newspaper clipping state it is a photograph: “A photograph of …”
Being clear, direct, and concise is essential to a well written image description. It can also be a challenge! This is why it is recommended to use Present Tense and Active Verbs as it will help to tighten up your description and make it tick all the right boxes. Check out Grammarly’s page on Active Voice for more information!
Grammar is very important to writing Alt-text. If your word choice and punctuation is wrong or off the screenreader will pick this up and your description will not make sense. You can not create paragraph breaks in Alt-text, so punctuation can be used to create pauses and structure.
Describe what you can see such as physical appearances and actions rather than intentions based on your interpretations or judgment calls. Never be subjective, the reader should be able to come to their own conclusions about any image.
Read the text around the image. If there is a person, place, or object that is named in the text, then use the name in your description. If there is a repeated character or place, only describe in detail the first time and then simply name the character/place in any following images.
Expressions can be tricky. Words and phrases such as “grinning”, “intense look”, or “serious expression”, might be somewhat interpretive, depending on the context. If possible, describe how the physical characteristics appear. For example, instead of saying “surprised look”, say “raised eyebrows and a wide open mouth”. Some words and phrases for expressions are more universal such as:
Skin tone, Age and Gender also needs to be objective. Go to Skin tone, Gender and Age to learn more.
Remember, you are creating a written description that replaces a visual image. The reader needs to be able to have access to what is important in that image, and this means we never censor image descriptions.