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.
In a society in which business is increasingly conducted online, excluding businesses that sell services through the Internet from the ADA would ‘run afoul of the purposes of the ADA’” in that it would prevent “‘individuals with disabilities [from] fully enjoy[ing] the goods, services, privileges, and advantages, available indiscriminately to other members of the general public.
“Streaming of video programming over the Internet—by defendant Netflix and other similar providers—has revolutionized the entertainment industry; it is fast becoming the dominant means of delivering movies, television shows, and other entertainment offerings to the American public. Persons who are deaf or hard of hearing should not be prevented from fully participating in this aspect of American life. Netflix’s denial of equal access to, and full enjoyment of, its “Watch Instantly” service violates the ADA.”-Assistant Attorney General, Thomas E. Perez.
The Department has assembled an official online version of the 2010 Standards to bring together the information in one easy-to-access location.  It provides the scoping and technical requirements for new construction and alterations resulting from the adoption of revised 2010 Standards in the final rules for Title II (28 CFR part 35) and Title III (28 CFR part 36).
Web designers often design in such a way that does not allow the user to adjust font size or color. While they may be protecting their brand, they are also inhibiting some users. Many visually impaired need to use high contrast color settings or very large fonts to read a website. Don't design your website in a way that makes it impossible for them to do this. 
The statement that “noncompliance with a voluntary technical standard for website accessibility does not necessarily indicate noncompliance with the ADA” is new and significant.  It is a recognition that a website may be accessible and usable by the blind without being fully compliant with the privately developed Web Content Accessibility Guidelines (WCAG) 2.0 or 2.1.  The statement confirms what some courts have said so far:  That the operative legal question in a website accessibility lawsuit is not whether the website conforms with WCAG, but whether persons with disabilities are able to access to a public accommodation’s goods, services, and benefits through the website, or some alternative fashion.