Let's say you take a photograph of your family with a camera on a tripod, so the camera is in an exact position. Next, without moving the camera, you quickly go change your clothes and get a haircut, and then you run back to the same spot where you took the first photograph. You take about a dozen photographs of yourself posing and smiling for the camera in the same spot where your family stood (but you stand just a few inches to the left or right).
Next you go home and open up a photo editor, and you crop the lone pic of yourself into the family pic. So it looks like you have an identical twin, and he has a different haircut and is wearing different clothes.
You print out this photograph and you keep a few copies of it, two copies in your car, one in your desk at work, two of them at home, and a minature version of it in your wallet.
So then if you ever get in trouble, you say "It wasn't me, I have an identical twin and he's an alcoholic, he always gets me in shit", and you show everyone the photograph.