Alt Text 

WebAIM Alternative Text provides alternative text examples and guidelines to help you label images correctly.

The alt text attribute should typically:

• Be accurate and equivalent in presenting the same content and function of the image.
• Be succinct. This means the correct content (if there is content) and function (if there is a function) of the image should be presented as succinctly as is appropriate. Typically no more than a few words are necessary, though rarely a short sentence or two may be appropriate.
• NOT be redundant or provide the same information as text within the context of the image.
• NOT use the phrases "image of ..." or "graphic of ..." to describe the image. It is usually apparent to the user that it is an image. And if the image is conveying content, it is typically not necessary that the user know that it is an image that is conveying the content, as opposed to text. If the fact that an image is a photograph or illustration, etc. is important content, it may be useful to include this in alternative text.

A "decorative" image is one that...

• does not present important content,
• is used for layout or non-informative purposes, and
• does not have a function (e.g., is not a link).

In many cases, you can ask, "If I could not use this image, what would I put in its place?" If the answer is "nothing," then alt=" is probably sufficient.