A snake is 0.1% of the picture.
On a 1920 by 1080 camera, a snake is about 70 by 40 pixels, often at night and half in shadow. A standard object detector downscales the frame to 640 pixels before inference, and the snake shrinks to a 23 by 13 smear. False positives are the opposite problem. Leaves, shadows and cables move all night, and at two frames a second across 70 cameras, the system screens about 12 million frames a day. If every leaf sends an alert, people stop trusting the alerts.
