You can't lose a defamation suit (or any lawsuit, yes, even in America) when *you limit your comments to provable facts*. If you are calling people names, or stretching the truth, you're going to find yourself in trouble. Maybe the problem is people don't know how to limit any public comment about an individual to facts alone.
I don't know about posting face photos of people who "attempted to shoplift" but certainly if you have video evidence of someone putting a turkey down their pants you can say "this person put a turkey down their pants". Where you might open yourself to a lawsuit is if you said they were "shoplifting" when they don't leave the store before being caught, or when they are not charged and convicted. Just stick to the facts; everybody will come to the proper conclusion.