Just describe whatโs in the pic. For example, gorgeous sunset photo with friends on the beach. Be descriptive of what the photo is that youโve posted. Does that make sense? If itโs a pet just described the pet and what itโs doing etc
This video might help you with defining what alt text is. However, I will admit that it's more specifically towards SEO, but it's super helpful for people who might need help understanding what text description is.