How to write Alt Text and Long Descriptions
- Alt text is not a rote description of the image. Instead it should convey the context and purpose of an image.
- Alt text is not the same as a caption, which typically provides information supplementing or not already in the visual element itself.
Figure 1: Example of an inspirational image
Without visual context, this caption does not tell the reader anything about what the image contains.
The alt text for this image may read:
Two hands holding a heart-shaped rock with the word ‘Hope’ engraved in it.
Successful alt text descriptions describe key elements and meaning in a way every user can understand. Unsuccessful alt text describes images in a way that is confusing or does not convey the educational goal of the content.
Alt text for a visual element can vary depending on how it is used. For example, the same image of New York City may be used within an architecture book and a book on photography. In the first case, the alt text may describe the construction elements and design of a skyscraper. In the latter, the alt text may discuss the angle of the sun reflecting off windows or the people walking by, or even what makes the photo “good” or “bad” from a photographer’s standpoint.
- Why is this visual element here?
- What information does it present?
- What is its purpose?
- If the image were removed, how would I describe it to convey the same information and/or purpose?
Alt text should be as objective as possible. Successful alt text follows some general rules. It is:
- Concise. Using a screen reader is time-consuming and unnecessarily long descriptions can create a burden on the user. Alt text should strive to be under 100 words, but never less than 10 words. Alt text on average is 25 to 30 words long.
- Targeted. Descriptions should reflect the context and intent of the image, matching the focus of the text, chapter, and title. The alt text may have different descriptions depending on its purpose in a work.
- Unique. Do not repeat descriptions or text already provided in the caption or the surrounding text. When images are completely described by their caption or surrounding text, consider identifying them as decorative images.
- Clear. Spell out all contractions, numbers, and non-Latin letters and present the information in a logical and consistent order.
- Simple. Screen reading software does not read formatting in alt text, so do not use formatting, such as bullet points, in alt text descriptions.
- Singular. Screen reading software indicates the alt text is a replacement for an image, so do not use redundant phrases such as “Image of...” or “Graphic of...”.
- Consistent. Use the same level and style of language used within the main body of text.
- Inclusive. Alt text should not contain additional information a sighted person (a customer not using a screen-reader) would miss.
- Complete. Conclude your alt text with a full stop/period (this allows for a pause in the screen reader before it continues onto the next body of text).
If your book contains non-Unicode glyphs and fonts, such as Arabic music symbols, the author should provide the meaning of the glyph or word. For example, Arabic music symbols would carry the Alt Text of: 'Symbol: Arabic half-sharp.' and 'Symbol: Arabic half-flat.'
Sometimes the caption describes the essential content and context of the image, rendering further alt text unnecessary.
Similarly, authors and contributors do not need to submit Alt Text for music notation. Music notation is difficult to describe using Alt Text and there is no best practice for writing these descriptions (yet), so Taylor & Francis will use a formulaic approach to describing the music's title and author within any book product.
- Long descriptions offer a more detailed description than Alt Text, and are usually required if the image provides further information that cannot be adequately described in the Alt Text and which is not already captured in accompanying body text.
- A Long Description is a detailed text translation of the image, which is objective, just like Alt Text. Successful Long Descriptions follow some general rules:
- Where Alt Text must be described within 10 to 100 words, long descriptions may be any length.
- Long Descriptions may contain lists and tables, but Alt Text cannot.