I remember trying to photograph the real bust (no flash of course) and a guard stepping in the way telling me it's prohibited.
Might depend on the person watching it, as museums tend to go... I witnessed someone nearly being ejected from the vatican museum recently, when they were visibly but not disrespectfully amused about a painting that was clearly made to elicit that response. Another person tried to take a picture and had to give their phone to the guard, who then proceeded to delete it and check if they took any others. I would've loved to watch that room for a while longer to see what else that guy was up to.