This document discusses using Fourier transforms to measure image similarity. It proposes a metric that uses both the real and complex components of the Fourier transform to compute a similarity ranking between two images. The metric calculates the intersection of the covariance matrix of the Fourier transform magnitude and phase spectra of the two images. The approach is shown to be advantageous for images with varying degrees of lighting. It summarizes existing methods for image comparison and feature extraction, and discusses implementing the proposed similarity metric using OpenCV. Sample results are given comparing the new Fourier-based method to existing histogram comparison techniques.