My guess is that it's not from a deleted scene. Freund was probably setting up a shot with Manners and Johann, when Karloff walked in and someone snapped the photo. Is it Jack Pierce? I wouldn't think so. Although Pierce would probably have been close by for touch-ups, he usually wore his white smock around the studio, and this guy is dressed like a carpenter. Additionally, Pierce always looked as if he had a large head, and this guy's head looks small, even compared to the woman sitting to his right.

And the films were not shot at the same time. MIRM was shot in the Fall of 1931, and THE MUMMY in the Fall of '32.