So I'm making a documentary style presentation for my English class, and I was wondering how you could cite an image or video source while it's on-screen.

I swear I've seen it done before in history documentaries, where some semi-translucent text will appear in the bottom corner, starting the source of the media currently being displayed. Does anybody know what I'm talking about? If so, do you have any examples? I'm mostly concerned about the format, but also would like a reference for the style.