University IT
Informative Images
Images that convey important information require alternative text (ALT text) so non-visual users can access the same information through assistive technology like screen readers. Including ALT text ensures all individuals, regardless of visual ability, can engage with your content.
The three key considerations for creating effective ALT text are:
Beyond these basics, other considerations apply.
Accurate
ALT text must accurately describe the image with correct spelling, grammar, and punctuation.
Common mistakes include forgetting to update ALT text when replacing an image or using file names like alt="image1234.png", which provide no meaningful description.
Concise
ALT text should be as brief as possible, with approximately 125 characters as a general maximum. Screen readers announce ALT text as a single uninterrupted block, unlike paragraphs where users can navigate word by word or character by character.
Equivalent
ALT text should convey information equivalent to the image's purpose. Imagine what you would say about the image if reading the page to someone over the phone. The ALT text depends on context and intent. For example, on the chemistry department website, the image below could have ALT text: "XPP Instrument Area Manager Daniel Stefanescu prepares LCLS instruments for beam and experiments in the Chemistry Lab on the historic Stanford University campus."
However, the same image could appear on pages about lab safety protocols, a new grant announcement, a professor's retirement, or other topics. The ALT text will differ in each case because the context and purpose of the image changes.
Other Considerations
Punctuation
Include appropriate punctuation in ALT text and end with a period or other closing mark. This adds a slight pause for screen reader users.
The exception is functional images like buttons, where the function alone is sufficient: alt="Add to Cart".
Avoid "Picture of" or "Image of"
Screen readers announce when an object is an image, making phrases like "Picture of..." or "Image of..." unnecessary. The exception is when the medium is important, such as alt="Painting of the Mona Lisa". The fact that it is a painting may be important to convey.
