When camera triggers on motion, Blue Iris sends Sentry AI the first frame of the motion clip. In some special setting and camera positioning, the motion is trigger first and human only appear many frames later resulting in false negatives.
One way to fix the problem is to define an area of interest (zone). In the sample image below, Blue Iris is configured to create a motion alert only if there is activity in front of the door.
This technique is very useful at front doors. If the camera is not positioned perfectly, then often times the camera triggers when the front door is opened but the person only exits the door many frames later resulting in many false negatives.