Hi,
In early model MacBook Pros the cable through the hinge (on route from Motherboard to Camera) could become frayed on well used models (open and closing the lid)
Later models have done away with that (rerouted cable) but suffer occasionally from the cable coming loose from the camera end.
If Apple Care is involved/available, I have seen posts were the whole screen is replaced (presumably for ease of access).
This is the sort of thing involved (this a a model Specific link)
Model listings
There have been suggestions that some people pick up or steady their laptop with a finger and thumb pinch top centre of screen where the camera is that may contribute to this.
Trouble Shooting an iSight suggest testing in as many apps as possible, then in a different Mac User account, checking the System Profiler before suggesting a SMC/PMU Reset
Some have found that a Safe Boot (and then Restart) has helped.
If none of the Trouble Shooting stuff down helps, it is time for an engineer.
9:29 PM Wednesday; August 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