The night vision lights (IR LEDs) on the camera may be reflecting off the glass or a nearby surface. Try repositioning and aiming the camera at a slightly different angle. If your camera is placed behind a multi-pane window, unfortanately it is not possible to avoid the IR reflection.

Below are a few alternatives: 

• Mount your camera outside
• Some cameras allow you to disable the IR LEDs while in night mode. You will need a 3rd party IR illuminator/floodlight for your camera to "see"
• Light up the area outside and put the camera in Day Mode (not auto).