Printing with a single colorant a security feature imperceptible to the naked eye. For a digital security image having a first region formed by a first pattern of binary pixels and a second region formed by a different second pattern of binary pixels, the first and second patterns are printed with the single colorant. A darker one of the first and second printed patterns is determined. The security image is printed with the single colorant, the region corresponding to the darker printed pattern printed at a reduced gray level such that the printed first and second regions appear substantially indistinguishable to the naked eye.