The number of CCTV cameras in the UK has been estimated at up to six million, most of which are installed in private homes and businesses. All CCTV cameras – whether the older, analogue type or the more modern, digital ones – have to make trade-offs between picture quality, storage and cost.
There are around 13,000 cameras in London Underground stations alone, and the footage from these is kept for two weeks. Upgrading all of these to record at 4K quality instead of 1080p would require an extra 300 million gigabytes of storage, not to mention the cost of the cameras themselves.
CCTV cameras also generally use wide-angle lenses to cover the broadest possible area. Digitally zooming in on a single person in the distance inevitably results in a blurrier image. Nevertheless, image quality is increasing all the time, and image processing software and machine learning algorithms can now recognise faces even from low-resolution video.