We investigate an all-phase-encoding technique in the input plane for security verification. In this technique, a primary amplitude image is first phase encoded and then multiplied by a random phase code. We investigate the performance of this technique by evaluating the discrimination between different biometrics images and between different random codes using Fourier-plane nonlinear filtering such as nonlinear joint transform correlators. The amplitude images can be any biometrics, and in this study we use fingerprints. We show that we can properly choose the nonlinearity of the filter and the coding weight for the random code to ensure good discrimination against unauthorized random codes and fingerprints. We also study the robustness of the all-phase-encoding technique to input image distortions such as rotation.