That is exactly my problem too. I only noticed the same thing when I updated to iOS 7.0.3. When I tapped on the HDR On/Off, the problem occured and I tried to reset the phone by pressing and holding the power button and home button simultaneously til the apple logo appeared. At first, doing this way fixed the rear camera issue but yesterday until today I have no luck. I just updated to iOS 7.0.4, I was hoping that this update will fix the issue but I was wrong. I have the same issue even with the latest update. Apple, wake up! I believe it has been an issue since you released iOS 7. Solve this mess, IMMEDIATELY!