Aloha Tatiana! I wish your questions had straightforward easy answers – and if you are government funded it kind of is. (See here: https://www.ada.gov/websites2_prnt.pdf) if you are not government funded, this is something that is currently being debated in the legal system. That being said, the WCAG 2.0 guidelines are a good set of guidelines to help protect yourself if you feel you should. (You can see more on WCAG here: https://www.yokoco.com/find-out-how-to-make-your-website-compliant/)
The Supreme Court decided under Title II of the ADA that mental illness is a form of disability and therefore covered under the ADA, and that unjustified institutional isolation of a person with a disability is a form of discrimination because it "...perpetuates unwarranted assumptions that persons so isolated are incapable or unworthy of participating in community life." The court added, "Confinement in an institution severely diminishes the everyday life activities of individuals, including family relations, social contacts, work options, economic independence, educational advancement, and cultural enrichment."
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.
Sometimes taking leave is a reasonable accommodation. The Family Medical Leave Act (“FMLA”) gives many employees up to twelve weeks of unpaid leave. This leave may be taken incrementally instead of large blocks of time, such as taking additional breaks during the day, taking half days off, coming to work later than normal, or leaving earlier. Taken a few hours at a time, twelve weeks can stretch out for a long time. An employer who denies FMLA leave may have violated both the FMLA and the ADA.
Web developers need to keep this in mind when creating websites. The best screen readers use naturalized voices and alter tone and inflection based on HTML tags, so choose layout elements carefully. It is also important to keep in mind that navigation is significantly slower when using a screen reader than it is for sighted people. Sighted people don't have to wait for the reader to get to the link we want- we spot links quickly and are able to navigate to our sought items, often without having to do any reading at all. Minimizing graphics also helps shorten reading times and speed navigation for disabled users.
While legal considerations might be your biggest worry, making your site more accessible is simply good customer service. More than 39 million Americans are blind and another 246 million have "low vision," Another one million are deaf in the U.S. Add to that people with mobility issues that prevent them from using their hands and that's a huge portion of the country's buying power.