Small is as small does.. . and costs. To collect any light the opening would have to be sufficient to allow enough light to excite the sensors. You are talking about a camera that would fit between the display pixels of your computer or mobile device. It would require lenses and a. CCD sensor of some complexity to resolve any detail at all.
On a 22" monitor, the standard pixels per inch is about 200. . . But those are composed of three actual LED lights, so your hypothetical camera lens would have to be smaller than 1/600th of an inch in diameter. . . Or youd have a distorted color pixel. . . Perhaps a dead pixel. Youd also have to have considerable circuitry on the matrix of the screen to handle the CCD plus graphic RAM and a radio of some kind to transmit the data, or an open port if using the internet, not to mention processor time which would be noted. Its not. Ergo, this hidden camera simply doesnt exist. By-the-way, the sheer cost of such miniaturization would likely dwarf the cost of every other component in the computer!
However, I wonder ... what about super tiny detectors between the display bits such that most of the tiny spaces between the display lights was taken up with the tiny detectors. And hardware and software collected all that detection together making the whole screen, essentially, a fairly high resolution camera. Conceivable??? Costly--sure--unless somehow it was engineered to be part of the same processes already laying down such layers of the screen.