You're deep enough if 1/2 squats are what you're aiming for. Your back doesn't look tight (ie I think it's in flexion, but I could be wrong), you should drop your head a bit and look roughly 6' in front of you. I won't even comment on the guy behind you, but the pins in the rack are there in case you fail a rep. That's just what my novice eye sees.
edit:
How much weight is on the bar? You might need to do a substantial deload to correct some of these issues.