I find Google Picasa to be the best amongst the "free". It can do much what a photographer wants for basic correction including re-sizing, cropping and etc etc. It does conversion with a very very slight loss in quality not visible to the naked eye. If you want to convert a jpg file into 100kb, of course there'd be a very very much loss in quality no matter what software you use. Where to put 'lah' the pixels info/data into such a small file?