Canon has created a 250-megapixel CMOS camera sensor. The sensor, which is APS-H size (29×20mm), packs a resolution of 19580×12600. By comparison, the highest-resolution commercial DSLR camera—the Canon 5DS and 5DS R—has an image sensor with "just" 50.6 megapixels, on a much larger full-frame (36×24mm) sensor.
It's important to note that Canon's 250MP sensor (actually 246.7 million pixels) is just a one-off, but it does actually work. Canon built a very basic-looking prototype camera (pictured below) around the sensor and whacked an SLR lens on the front. During testing, the monster sensor (combined with optical and digital zooming), was able to "distinguish the lettering on the side of an airplane flying at a distance of approximately 18 km (11 mi) from the shooting location."
Beyond sheer pixels, the new sensor is also capable of ultra-fast signal readout (i.e. getting the captured image data out of the sensor and onto the main system bus). Canon claims the sensor has a readout speed of 1.25 billion pixels per second, enough to shoot 250MP images at 5 frames per second. There will have been some very advanced digital signal processors (DSPs) involved in such a feat, but unfortunately Canon isn't giving any specific details at this point. By way of comparison, the 50MP 5DS is capable of shooting at 5 FPS, or a readout speed of around 250 million pixels per second.
Canon doesn't mention it in its rather spartan press release, but the files produced by the 250MP sensor must be absolutely huge. A single RAW image from the 5DS (8688×5792) comes in at about 70MB. Thus, a single image from the 250MP sensor would be about 350MB. Saving five of those per second—about 1,750MB/sec—would be rather taxing. You'd need something like an M.2 SSD. None of the current CompactFlash or SD card standards would get close to 1,750MB/sec.
While this 250MP sensor won't be coming to market any time soon, it's pretty safe to assume that it will arrive in a DSLR or some other high-end imaging device (medical, surveillance) eventually. Back in 2007, Canon showed off a prototype 50-megapixel sensor; and now, eight years later, there's the 5DS. In 2010, Canon had upped the prototype ante to 120 megapixels. If Canon manages to squeeze out a 120MP DSLR in 2018, then maybe we'll see a 250MP camera by 2023...