When Alex takes the handsome stranger back to her apartment, she removes her jeans whilst he sits on the bed watching her. When Alex leans forward to kiss him you can see that she is wearing the jeans which she had removed only a few seconds before.
After Amber Smith's character comes home to find the suspicious staking photos left for her in the manila envelope, she goes to ask her roommate/lover if she saw anything. In the back round you can distinctly see the camera man catching the shot in the hallway mirror.