Quality alt text is critical for images used on your webpages.
Generally, the alt text needs to describe the image. If the image contains text, the alt text should contain that text. If the image is a scene, the text should describe that scene to convey it to a limited sighted visitor.
An exception to these guidelines is for an image that is the only item inside of a link. If the link does not contain any text, the alt text of the image should describe to the user the destination of the link.
If an organization's logo is featured on your site AND the logo is linked to the about page of that organization, AND there is no text within the link; the image's alt text should read "About the Organization" instead of "Organization Logo".
If you have an image of a graduate that is contained inside of a link to a commencement page, and that link also doesn't contain text, the image's alt text should read "20XX Commencement".