1. A computer-implemented method for determining a biometric score, the method comprising: receiving at least one image of an eye, the at least one image comprising a view of vasculature of the eye; determining at least one metric for the at least one image, the at least one metric comprising a first metric representing an extent of detected vasculature in the at least one image based on a plurality of color difference signals determined from color components of the at least one image; and calculating at least one score for the at least one image based at least in part on a comparison of the first metric with a corresponding metric of a reference image.