You need to give credit card as security deposit. This money they will block. They will use it only if you run away without paying any traffic violation. Blocking is safe as you will be having receipt for it. Regarding, photocopy from front side is ok but make sure you put some sticker on 3 digit security code (CVV) on back side of credit card before photocopy. Never give this code to anyone, without this code no one can use your credit card online.