size difference
Images that focus heavily on the size difference between two or more people; often minigirl, miniboy, giantess, and giant male pictures fall into this category.
If the 'natural' difference in size between characters, ie. 'short' vs 'tall' is the focus of the picture, use height difference instead. If one person has a small body overall, they are petite.
Focusing exclusively on breast or muscle size difference is breast envy and muscle envy instead.
For an image that has been changed from its original size, use resized.