Geometric Shapes. Use this one with Hough Transforms. The other two images are too large for transform space allocation. This is a Java Applet limitation and would not exist in a stand-alone application.

Buildings. This is a nice image for point transforms. Most pixels have high intensity, so the image is too bright. Using a point transform, one can noticeably increase the contrast by distributing the intensities more evenly.

Water Lilies. This is just a pretty picture. One can create a nice watercolor-like effect using rank smoothing.