In journalism, the “cutline” is the text below a picture, explaining what the reader is looking at. It’s what most people call a caption, but to a journalist, a “caption” is more like a title that appears above the photo, while the “cutline” is a few lines of text under the photo.

An AP style caption is usually two sentences, with the first answering the question “What, exactly am I looking at?” (with names of the one or two most important people in the photo, the location / event, and date) and the second answering the question “Why is that newsworthy?”  Space is limited; brevity is golden. 

Same picture, different cutline. Here the reader learns something new, though the detail seems a little random.

A much more effective cutline builds on the photo to draws the reader into the story.

I found these great cutline examples on ibiblio. 

Update, 10 May 2023
     Links to ibiblio now come up as “403 Forbidden.
     Added link to Janet Walsh’s description of AP photo captions.