Chosen Solution
I replaced broken glass screen on my iPad2. Digitizer was working fine. The iPad functions well with clear glass but the rear camera is neither working nor recognised. Front camera works normal. What could have gone wrong?
You may have damaged the rear camera flex cable when removing the screen or reassembling. The camera is easy to remove once you have the screen off, iFixit has a guide. Check the cable carefully to see if there are any nicks or damage to the cable. You could also just try reseating the cable in case in came loose.
