Can a firewire camera use Photo Booth's backdrop effects?

I plugged in a firewire camcorder, and it works with Photo Booth, but when I attempt to use the backdrop effect (keying out the background), it instantly says, "Backdrop detected," shows the backdrop image or video, but doesn't show any action that's happening in front of the camera. Any idea what's going on? Or is there any software that replicates this backdrop effect functionality? Thanks!