The type of people that are prepared to leave a restaurant without paying are not worried by CCTV cameras. They are prepared to be physical to the point of violence if anyone attempts to stop them and then, in the rare event that the Police are called, if the Police arrive in time, or if they are identified to the Police, they then claim that the food/meal etc was inferior or poor quality and that they were not prepared to pay; it then becomes a civil matter, i.e. exchange names and addresses and the restaurant has to take civil action to recover the money, and no restaurant is going to do that.