process hangs
ImageMagick can appear to hang if the image is large. In this case, the pixels are forced to disk and since disk is much slower than memory, the process can take a long time (sometimes hours if its a large image). If you are sure all your images are of reasonable size (e.g. less than 1000 x 1000 pixels) we cannot think of any reason the process would hang. Definitely try an upgraded version (the current release is 6.2.7-1) and if it continues to hang, let us know. With the upgrade, use -resize instead of -geometry.