Your site would need to have a text only option, with all functionality accessible through a keyboard for visitors with mobility issues. Once you make these and other changes to meet ADA guidelines, your site would need to be tested by a website development company familiar with ADA compliance issues to be sure that visitors who use assistive technology such as screen readers are able to access your web content fully.
This is the reason why I think web design firms have to position themselves as solution providers and not just web guys/gals. A client doesn't need a website, they need sales. The website is just part of that solution but it's not the solution and unlike web design, service like email marketing automation, SEO, and PPC requires an experienced professional.
When the law was enacted in 1990, it did not specifically address website accessibility for the disabled, but this has become a much-discussed topic in recent years. In 2006, Target settled a class action lawsuit alleging Target.com was inaccessible to the blind, in violation of the ADA, and in 2015 both Reebok and the NBA were hit with a class action lawsuit that alleged their websites did not accomodate the blind and visually impaired.
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.