A profile detector in a scanning system measures spacing of an original non-planar image from a reference image plane of the scanning system. The spacing is measured by projecting a spot of light, with a collimated light source, onto a scan line of the original non-planar image at an angle that is oblique with respect to the fast scan direction of the scanning system. A first photosensor converts optical information reflecting off of the original non-planar image at a first slow scan position into electrical profile data. A position along the fast scan direction is identified for the first slow scan position by locating the spot of light in the electrical profile data. The located position is compared with a pre-recorded position along the fast scan direction for the first slow scan position. The pre-recorded position defines a position where the first photosensor would have detected the spot of light if it reflected off of a planar image. The difference between the located position and the pre-recorded position is used to determine the value for the spacing between the original non-planar image and the reference image plane at the first slow scan position. In a one pass scanning system, a second photosensor records image data at a second slow scan position that is offset from the first slow scan position. The offset provides sufficient time for the scanning system to calculate the spacing of the original non-planar image from the reference image plane before the second photosensor records image data at the first slow scan position. In a two-pass scanning system, the first photosensor records the image data during the second pass. The scanning system compensates for image distortion caused by the calculated spacing by either adjusting system scan parameters or by performing image processing techniques.