Its called a picture within a picture
The term is inset.
A picture that has a smaller copy of itself within the picture, with the copy having an even smaller copy, that continues to (theoretically) infinity, is called a Droste Effect or recursive picture.
If it's a picture of the same picture then it's known as the Droste effect. But a more generic for this is just a recursive picture.
Wla
That's an "inset".
1. Droste effect2. mise en abyme
Inset.
dog
picture graph
Is called a glyph.
A caption.
That is a picture that has 1 mega bite of space within itself.
It is called an Avi (avatar) or DP (display picture.)
A thumbnail picture
This picture is called "pictogram".
The picture is called "tennisball."