It's going to be tough phone to fix if it is not software related.
Have you tried clearing the cache in the camera app? Long press on the camera app until you see the pop-up, click on the "i" go to storage and clear cache. If that doesn't work, try to wipe cache partition. The last thing is locate a Samsung service center near you and see if it can be repaired.
It might not be worth fixing considering the phone is over 5 yrs old and out of software updates, you might need to upgrade if they can't supply the parts to fix it.
