iPhone has photos/videos which I didn’t take, has it been hacked?
The camera can be used from the lock screen without unlocking the device. Access to existing photos is unavailable without unlocking, but new photos and videos can be taken without unlocking the iPhone. Your device has almost certainly not been ‘hacked’.

From the lock screen, swipe from right to left to access the camera. Photos taken here are added to your camera roll as if you’d taken them unlocked.