1. A machine for processing successive n.times.n arrays of digital data, which data represents two-dimensional images, for the purpose of detecting image corners comprising: (a) two-dimensional Haar transformer means for Haar transforming the digital data in two dimensions into successive n.times.n arrays of transform coefficients, (b) comparator and thresholder means having a preselected threshold set therein, (c) a read-only memory containing a list of transform coefficients that are sensitive to corners, the output of said read-only memory being fed to said comparator and thresholder means, (d) said comparator and thresholder means comparing the preselected threshold with the absolute magnitude of each of the transform coefficients that are sensitive to corners, and outputting an indication of a corner together with the transform coefficient and its address whenever the absolute magnitude of the transform coefficient exceeds said preselected threshold.