What in the world are these boxes called, please?

The boxes (one might say like a dialog box) can contain cartoons, graphs, wise or funny sayings or political satire or genre of quips, etc, etc. Most people, for instance, on Facebook employ/post these boxes that contain sayings and such, all the time. Like, one might have a box that says: SUPPORT THE TROOPS and have a US flag in it or some such. Anyway, I hope you can understand what I'm trying to explain. Please tell me what the boxes are called.

Thanks tons!!!

May