Method for detecting rotation and magnification in images

A computer program product, comprising a computer readable storage medium having a computer program stored thereon for detecting an amount of rotation or magnification in a modified image, for performing the steps of:

• a) embedding a marker image having a pair of identical features separated by a distance d and oriented at an angle .alpha. in an original image to produce a marked image, the marked image having been rotated and/or magnified to produce the modified image;
• b) performing an autocorrelation on the modified image to produce a pair of autocorrelation peaks corresponding to the location of the features of the marker image in the modified image;
• and
• c) comparing the separation d' and orientation .alpha.' of the autocorrelation peaks with the separation d and orientation .alpha. of the features in the marker image to determine the amount of rotation and magnification in the modified image.