One of the simple techniques is to see the path lengths of all the traces. If there are traces with significant number of longer paths, that is a clear indicator that there is an image in the file. The trace lines where the traces are longer are the approximate location for the images. Another approach that could be used is to compute the derivative of the trace paths and detect major deviation locations in the trace paths. These deviations occur when there is an image in the trace path. The start of the high derivative location is close to the approximate location of the image.