It's the difference between a caption and a description. Both are useful, just in different settings. A visually-impaired person reading the newspaper just wan

It's the difference between a caption and a description. Both are useful, just in different settings. A visually-impaired person reading the newspaper just wants to know that there is an image of, say, George Washington and John Adams. What do they look like? What are they wearing? What is the setting? Probably not important, it's just decoration for the article. On the other hand, a visually-impaired person who's shopping for clothing might come across a t-shirt with a print and want to know what's on there. What colors are used? Is there any text? Are there logos? Stuff like that matters when you're choosing clothing because you don't want to end up looking like a clown.