Where can I find stock Android apps that are not normally in the Market?
So I just looked at the firmware for my Samsung Vibrant, you don't actually need to mount the image -- I was thinking of the recovery image or a nandroid backup.  The firmware (ROM) should be in a zip file, which you can open up and go to /system/app/ and grab the camera.apk.  I'd put it on your phone's SD card, then use Root Explorer or similar to copy it into /system/app/ on your device and overwrite the current one (which you may want to back up first).

You can check out my answer to another question for info on mounting, but you shouldn't have to do that :)