Try going to Settings > More > Application manager > All and then go into the Camera or Gallery app and try Clear cache and Clear data. If it’s still running you may also want to Force stop it.
You can also try wiping the cache partition
1. Turn the S4 off
2. Press and hold Volume up, Home, and Power together.
3. When the phone vibrates, let go of Power.
4. When the Android Recovery screen appears let go of Volume up and Home.
5. Use Volume down to highlight wipe cache partition and then tap the Power key to select it. It should automatically restart after wiping it.