1. A distortion invariant method of detecting the presence of one or more predefined targets in an input image comprising: correlating the input image and a synthetic discriminant function (SDF) reference image obtained from a plurality of training images in a shift phase-encoded fringe-adjusted joint transform correlation (SPFJTC) correlator yielding a correlation output; determining a peak-to-clutter ratio (PCR) for the correlation output; and comparing the PCR to a threshold value such that one of the predefined targets is present in the input image when the PCR is greater than or equal to the threshold value.