Hi Katie,
Auctiva hosts the Auctiva Store images as one of several that are automatically created on upload. In fact that is a 96x96 image (the mystery on use and its storage tag is solved, but that's another post). I have sometimes seen delays on that one updating after you've uploaded a replacement (used Replace feature in Image Managment). It's possible that one updates (rebuilds) on the same cycle as updates to prices, etc. for store, but that's a guess.
Danno