During Lucy Sheridan's striptease sequence, her knickers change from black to white to black again.
During the opening murder, the killer's trousers change pattern between shots. They are plain grey outside the building, and checkered as soon as he gets inside.
During Lucy's photo shoot, whenever we see a close-up of the photographer he is always aiming his camera downwards. Presumably, these inserts were shot when Lucy was lying on the ground, but they are edited in such a way that it looks like he's photographing the floor whilst she is standing up.
During the meeting at Speaker's Corner in Hyde Park, a lot of the passers by are looking straight into the camera. Some of them actively try to get on camera, whilst others are startled and turn away.
When Holbourne and Morgan visit the outdoor crime scene at the abandoned stables, the coroner tells them the murdered model has been dead "about 2 or 3 weeks". It's extremely doubtful no one would be wearing masks or displaying some revulsion from the stench of a body in that advanced state of decomposition.
There is no way to take an x-Ray of a face just from a photograph.