1. A method for generating a printed security image on a banknote, said image comprising an original image and a security pattern, wherein said security pattern obtained in the spatial domain by the inverse Fourier transform of the combination in the frequency domain between the Fourier transform of an auxiliary image and a radially symmetric, two-dimensional pattern, said two-dimensional pattern created by sweeping as self-similar, one-dimensional function along a 360-degree arc, such as said security pattern being detectable from the maximum value of the cross-correlation of said one-dimensional function with the Fourier transform of one line of said banknote, said line being sampled along any arbitrary direction and with any resolution between 50 and 1200 dots per inch, the security image being generated in the spatial domain by the merging of at least one color of at least a part of the original image with the security pattern.