Pragmatic solution is a port of libjpeg-progs_6b-10 and use the following:

/media/mmc1 $ djpeg -scale 1/2 Images/Sample.jpg | cjpeg Small/Sample.jpg

This gives a 1408x1056 image in a few seconds. Using '-scale 1/4' would give a 704x528 image. So either a bit too big or a bit too small but less effort than just right!