For YEARS I have done all simple graphic manipulation using a free program called
IRFANVIEW. Weird name, but unbelievably powerful program. It's not only the best conversion utility around, it has "batching" capability meaning you can aim a conversion command at an entire folder full of pics and get converted pics.
On top of that, it does everything else you could want in terms of simple manipulation... resize, crop, reformat, tons and tons of tweaking tools.
It's the best screen capture tool around, too.
Lastly, it's got "plugin" capability, so recently there have been a slough of additional features added. I even use it as my baseline sound clip player. Cool little tool.
IrfanView - Official Homepage - one of the most popular viewers worldwide