From: The World In Your Head by Steven Lehar

Fig. 3.2 The dog picture is familiar in vision circles, for it demonstrates the principle of emergence in perception. The local regions of this image do not contain sufficient information to distinguish significant form contours from insignificant noisy edges. As soon as the picture is recognized as that of a dog in the dappled sunshine under overhanging trees, the contours of the dog pop out perceptually, filling in visual edges even in regions where no edges are present in the input.