I'm willing to imagine that the use of this proposed feature *could* be amusing and/or interesting, but constant repetition would make it less amusing. So I don't really like the idea of a fixed, small list of images: small list => boring. Unfortunately, allowing any image url will get into, um, other problems. I have no solution to this problem.
On the other hand, allowing for a lot of use of this feature, will make it boring through acclimatization. If we allow only those of an exalted rank to use this, I expect that we will not see enough use of the feature to make it worth implementing. However, I do have a suggestion on how to control the use: make it cost all your daily votes.