Widget5 - Image-processing package that supports 256 grey level (8bit), 65536 grey level (16bit) and 16.7 million colour (24bit) images. - http://www.orac2.demon.co.uk/software/widget5/widget5.html
Variations - Applies a range of changes, to a greater and lesser extent, to an image, showing 9 possible outcomes. - http://compo.iconbar.com/variation.htm
DA's Picture - [Freeware] Formerly commercial package for OS 3.5 and above. - http://www.arcsite.de/hp/dapicture/indexuk.html
Sfmerge - Very simple utility that merges several sprite files into one. - http://www.armware.dk/files/sfmerge.html
Mksprite - Makes pretty optimal sprite files from draw and Euclid files. - http://www.armware.dk/files/mksprite.html
David Pilling - Includes TWAIN drivers, and ImageMaster, an image editing program. Both are commercial software. - http://www.netlink.co.uk/users/pilling/