ADA compliance means making your place of business fully accessible to persons with disabilities. The Americans with Disabilities Act (ADA) was signed into law in 1990, but it only covered brick and mortar businesses. Meaning your place of business had to accommodate people with disabilities. Now that technology has advanced, this law applies to your web site as well.
The words in the tag should be more than a description. They should provide a text equivalent of the image. In other words, the tag should include the same meaningful information that other users obtain by looking at the image. In the example of the mayor’s picture, adding an “alt” tag with the words “Photograph of Mayor Jane Smith” provides a meaningful description.