i have had the same problem as well.My iPhone 4 rear camera all of a sudden went blank and it freezed when i tried to swipe through it. I went to http://tcawireless.com/ where they told me to try turning iPhone off and then back on. They also told me If the camera does not show up in the search, check to make sure that Restrictions are not turned on by tapping Settings > General > Restrictions. In my case it was third party app which was interfering with the autofocus/exposure feature and the flash and that is why I was facing image quality issues with photos. Third-party cases can interfere with the autofocus/exposure feature and they told me to remove the case and the flash (iPhone 4 only); try removing the case if you have image-quality issues with photos. I hope this will help.
I recommend you take it to your nearest apple store and ask them to recommend a repair company. Rather than choose one off the internet that may or may not be able to fix it for you