Recently I wanted to switch from Adium back to iChat to take advantage of the video chat feature. To my disappointment, iChat AV 4.0.x in 10.5.8 did not work with my USB webcam, even after installing iUSBCam (formerly iChatUSBCam). For some reason, iChat was not detecting my USB webcam.
I searched in vain for a workaround and hacks. Eventually, I read a related suggestion on another message board about looking at the Console log for processing history. I searched there: nothing; but it did lead me to learning how to find out what processes were in action, in greater detail than Activity Monitor.app provides.
I used sudo lsof in Terminal to scan through a list of the processes in action. I used this command both before and just after starting iChat. Much of the screen text was too complicated and irrelevant to my current plight, but I did notice that QuickTimeUSBVDCDigitizer.component is used for the built-in iSight, and it's located in /System/Library/QuickTime.
This led me to wondering about another USB webcam plug-in that I've used before, maccam. Sure enough, the maccam plug-in component was in the /Library/QuickTime folder. Then I thought, wait a minute. What about installing a copy of this maccam component in the System folder's QuickTime folder?. So I placed the maccam component into the /System/Library/QuickTime folder.
Success! iChat AV 4.0.7 recognized my USB webcam and my PhotoBooth worked as well.
Mac OS X Hints