1. An image-change detector comprising: a photodetector array of pixels; a phase grating to receive incident light, the phase grating to induce near-field spatial modulations responsive to a point source, the modulations illuminating a pattern over nonadjacent ones of the pixels at the photodetector array responsive to the incident light; and logic coupled to the photodetector array to successively poll the pixels to produce sets of image data, and to compare the sets.