Is it not as simple as to add a "Trash" function? It's been around on operating systems for years, everyone understands how it works and that you can restore something from the trash, but you lose it forever if you empty the trash.

Since this is something that's trivial to implement and is a UI principle that's extremely common, there is absolutely no excuse for keeping images around where the user wants to delete them. If you're annoyed at a dozen emails a month, you implement that and then you can easily respond "Wait, you sent it to trash bin, then deleted it, and NOW you change your mind?", in more polite terms.

(Edit: sorry, late for the party, I was linked here from another post on the same subject)