I use a little program called Irfanview
http://www.irfanview.com/
When you open the image, resize it to the size you want, then click on File, then Save as....
Then click on the button that says Options.
Where it says KPG Save Quality, move it to about 70%.
Then click OK.
Then save the file.
It should save most images that aren't too big at less than 100kb.
Hope this helps some.