Rather than cropping the picture, you can simply re-size the picture. Simply I mean if you have a program to do so. Dee uses a full version of adobe, and I have a little sub-utility that is built into the software I use for my profession. I know there are cheap or free utilities that can do this, possibly even using ms paint or something in the standard suite you usually get with you computer.
What these do is just change the way the file is saved. retaining the picture, but telling it how to display the picture by number of pixels per inch, and the actual size of the picture itself. You can take a huge picture and shrink it to avatar size, or even blow one up, but blown up it gets grainy, shrunken it loses some detail.