Hi,
The Effects and Backdrops are Quartz files (they take the camera feed and work their magic)
They are held in the System/Library/Compositions Folder and are used by iChat and the Photo Booth app.
Do you have the same issue in iChat ?
So...
The Compositions folder could have been emptied somehow.
It could have been moved so that Photo Booth cannot "see" it.
Photo Booth could have a fault.
Do you have the Quartz Files ?

9:15 PM Saturday; September 17, 2011
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb( 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously