Alt text, which stands for “Alternative Text,” is important for people with visual disabilities because screen readers use it to describe what is in a picture. Google also uses the alt text to determine what a picture contains, allowing people to search for images based on keywords.
When inserting images into your site, always fill in the right-hand-column boxes for both title and alt text. To create alt tags, try to write no more than one-sentence descriptions that are detailed but not wordy. For example, the above picture shows the WordPress Insert Media screen with an image of HMS about to be inserted into the page. For this image, you could write the following alt tag: “A HDR photo of the Harvard Medical School quad looking towards Gordon Hall on a beautiful summer afternoon.” The sentence is concise yet fully describes what the photo shows.
In the right-hand column of this same screen, notice the other boxes for media information:
Title (This box should always be filled in.)
Titles refer to the names given to media. A title is displayed in the File column of the Media Library Screen and is often shown on attachment pages and galleries if themes or plugins are designed to display it. Titles should be descriptive but kept short (a maximum of 5 words). The title for the example photo above might be “HMS quad and Gordon Hall.”
Captions are brief explanations of media. A caption will display underneath an image in a caption box.
Alternate Text (This box should always be filled in.)
How to fill in the alt text box is covered in detail above.
This box is for longer descriptions of media. Use it to describe an image in substantial detail or to add more keywords. The contents of this box will not be displayed publicly.