Techniques are described for authenticating security documents having security images that incorporate multiple security features. The techniques may produce robust template matching results in situations of lighting unevenness, even with stronger occluding objects. The techniques may be particularly useful in validating a security document having a security image composed of one or more “virtual” retroreflective images formed over a background of a repeating retroreflective image. The virtual retroreflective images within the security image provide strong signals that may dominate analysis and validation of the background retroreflective image, thereby resulting incorrect authentication. The techniques provide a modified normalized cross-correlation analysis that masks out the strong signals contributed by the additional security features, such as the retroreflective virtual images, while still allowing for fast and efficient template matching to be performed with respect to the background image.