mise en abyme
Mise en abyme is when an image (or part of an image) contains a copy or altered version of itself, which thus contains another copy of itself, and so on seemingly forever.
This can mean that the image depicts an object (such as a painting or a computer screen) which happens to be a copy of the entire image; this is the Droste effect. Another example is if a character stands between two parallel mirrors and thus sees an infinite "mirror hallway".