There are more than 4.5 million of them in the UK, but CCTV cameras are failing to cut crime, a senior police officer has claimed.
Detective chief inspector Mick Neville of the Metropolitan Police said that the devices helped solve less than 3% of street crimes such as robbery.
One of the biggest problems is that criminals were not afraid of cameras, as they assume they are not working, he said.
A recent Home Office report on CCTV revealed that up to 80% of footage gathered was "far from ideal" for police use.
He added that officers also needed more training in how to use footage.