These statistics are especially important when you consider the potential spending power of people with disabilities. Unfortunately, if the website isn’t accessible, then it is excluding more than 60 million Americans14. Additionally, 71 percent of customers14 with disabilities will instantly leave the site if it does not meet their accessibility needs. Another 80 percent of customers14 with disabilities have stated that they will spend more on a website that has improved accessibility features. Fortunately, if you follow Web Content Accessibility Guidelines (WCAG)7, then you can appeal to millions of individuals who want to enjoy the same online experiences as their friends, family, and neighbors. Giving them the chance is not only right, but it is also in accordance with ADA regulations.
The gray area is a matter of scale and purpose. If you have a small business which serves as specific market it's a good idea to make the site as user and disability friendly as possible. If, however, your market serves segments with a likeliness to have various handicaps or disabilities you should address that with an ADA Compliance review of the site. Also consider the scale and purpose of an organization. Publicly traded large businesses need to concern themselves more than a single location family owned retailer and if someone sues your flower shop because the text was too small or didn't have "image alt tags" causing them distress... That's pretty frivolous and would likely not stand.
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.