What is the point of a caption for a photo in a magazine?

A caption is actually quite useful: it explains what is in the photo, as well as who is in it. And it sometimes gives additional information that helps the reader to understand the story better. Yes, some photos are pretty obvious (if I write an article about Lady Gaga, and there's a photo, you would expect it to be a photo of Lady Gaga). But even the obvious can require a caption-- so, when was this photo taken? Is there anything unusual about it? The caption can provide additional information that enhances the story: "In this 1999 photo of Lady Gaga, we see her at one of her earliest auditions." Also, to avoid plagiarism, many captions include the name of the photographer, or the agency that provided the photo.