1. A method of verifying the authenticity of an object, the method comprising: encoding a primary image; convolving the encoded primary image with a random code, generating thereby a first reference image; transforming the first reference image; and correlating the first reference image with a second reference image; wherein convolving the encoded primary image with a random code comprises convolving the encoded primary image with a random code that is the Fourier transform of a phase-only uniform random distribution.