As drones get cheaper and cameras more advanced, we are more easily under surveillance than ever.

Now Canon has revealed a 250-megapixel APS-H CMOS sensor that can distinguish letters on the side of a flying airplane from 12 miles (18km) away.

The sensor could one day be used in spy cameras.

Canon has announced a new sensor (pictured left and right inside a camera) that could be used in future spy cameras. The Japanese camera giant claims the 19,580 x 12,600-pixel sensor sets a world record for resolution in its size

The Japanese camera giant claims the 19,580 x 12,600-pixel sensor sets a world record for resolution in its size.

With CMOS sensors, increases in pixel counts result in increased signal volume, which can cause such problems as signal delays.

But the APS-H has a fast signal readout speed of 1.25 billion pixels a second and is said to produce crisp images.

The 250-megapixel APS-H CMOS sensor can distinguish letters on the side of a flying airplane from 12 miles (18km) away. A stock image of a plane in flight is shown

As well as taking photos from an incredible distance, the sensor allows photographers to capture incredibly high-resolution video at a speed of five frames a second.

More importantly, footage is shot at 30 times sharper than 4K (3,840 x 2,160 pixels) or 125 times that of Full HD video.

Videos can be cropped and magnified without sacrificing image resolution and clarity.

Canon says the sensor could one day be used in ‘specialised surveillance and crime prevention tools, ultra-high-resolution measuring instruments and other industrial equipment.’

This means that while spies may get their hands on the technology, it will probably not appear in a standard DSLR camera in the near future.