More than likely it was a jumper that was damaged during the repair. I have seen this MANY times. However, I have only personally seen it with the GSM iPhone 4 and it is easily fixed. On the CDMA 4 and on all 4S models I have not been able to locate the jumper on the logic board.
Let me ask this, do you have Instagram? Or a 3rd party camera application? If not, download Instagram. Try using the camera on it now.
If that doesn't work, try restoring the settings, then use instagram. See if either of those works. let me know