We can smile in driver’s license photos but smiling in a mug shot is a psychological move. Whenever you see someone frowning or straight faced in a mug shot you have a perception that that person is bad because they look mean. A smiling person seems like a happy person or someone that is likeable. This is why smiling is infectious. It’s seen as a positive thing. More impressionable people or easily deceived people will not think twice about it and fall for it. What matters is that you see it and not just in the mug shot but in all aspects of life.