Re-sizing a picture

Here's a general question.

How do I re-size a picture (of myself) to the forum requirements of 50 by 50 pixels or 19.5 KB for my Avatar picture?

I've tried fooling with the attributes on some test pictures but still can't get the desired results.

Thanks in advance.

I normally find a pic I like, whether its a snap shot or something else. I open it with the Gimp and scale it to 50x50 pixels.
If I am at work I have to edit it with paint and do guestimates at how big it is.

Than just upload it.

Oh, and it will go a bit pixelated if you are resizing and not cropping, but don't worry about it, once you have it in the profile or whatever, it doesn't look pixelated at all.

Thanks!

For those who use a mac, there's a handy widget called Image Shackle. If you just want to quickly resize for a (ex) forum pic, you just drag the original to it and choose the pixel size you want. Takes 2 seconds.