User Behavior and Image Cache

Hi all, I have a collection of different images with android.gallery3d/cache and android.messaging/cache/image_manager_disk_cache source files which appear as modified over the span of a week (so I don't believe they were cached at the same time): editing to add that it's the same three or four images that are appearing multiple times as cached on different days and different times during the course of a week.

I'm trying to figure out the user behavior that would cause these images to be cached, assuming it's a user thing at all and not just something prompted by the device. My searches have thus far not turned up a definitive answer; is this something anyone else has knowledge around? Many thanks.