1. A method of comparing a first image and a second image comprising the steps of: (a) compressing the first image into a first image projection; (b) compressing the second image into a second image projection; (c) determining a deviation of symmetry of the first image projection and the second image projection by the steps of: (i) locating a correlation peak &Dgr;; (ii) performing a correlation function at a first point near the correlation peak &Dgr;&plus;&dgr; to determine a first correlation result; (iii) performing the correlation function at a second point near the correlation peak &Dgr;−&dgr; to determine a second correlation result; (iv) performing the correlation function at the correlation peak &Dgr; to determine a peak correlation result; (v) computing a difference between the first correlation result and the second correlation result; (vi) dividing the difference by the peak correlation result to determine the deviation of symmetry; and (d) comparing the deviation of symmetry and a predetermined threshold value.