An ALT attribute is a tag used within an <img> tag in HTML to describe to search engines what the image actually is. It's also useful for visually impaired users, who may be using a text-based browser, and users who have images disabled.
An example of an image tag with the ALT attribute set is below:
<img src="logo.png" alt="Image of company logo" >
To set these up depends on where your image is and how you have added it to the page:
This plug-in will automatically output the ALT attribute based on the group description.
This does not appear to output ALT attributes yet.
Images in HTML Layouts (Templates)
In Prospect's CMS Editor, you can edit the HTML of the layouts and add in any missing ALT attributes to your images under Home > Layouts. This will open a new window, allowing you to add the missing ALT attribute.