The first demonstration of ghost imaging, performed by T. B. Pittman, Y. H. Shih, D. V. Strekalov, and A. V. Sergienko in 1995, was based on quantum correlations between entangled photon pairs. One of the photons of the pair strikes the object and then the bucket detector while the other follows a different path to a (multi-pixel) camera. The camera is constructed to only record pixels from entangled photon pairs that hit both the bucket detector and the camera's image plane (as opposed to entangled photon pairs where one hit the image plane but the other does not hit the bucket detector, which are not registered). Then a large number of registered entangled pairs gradually forms a full image.