It's sort of a trick question, even though it isn't meant to be. Corsets changed their shapes and objectives so many times through history that without knowing the type of corset in question, it's pretty impossible to say.

The shape of the boning is visible on the second one. The general shape seems to make it obvious too. But maybe people who are unsure are assuming it's an underbust style giving support on the left? Still, I personally thought I was pretty obvious and I've never even worn a corset. Just someone who admires old, beautiful clothing XD