I always go into paint, click on "image" on the top panel and click "attributes" when your picture is open. That will tell you the pixels by pixels of the current picture. It needs to be 100 by 100 (really small). Then go to Image, stretch/scew to change the size by percent. Mess around with it until you get it right. You might have to shink it upwards or from the side to make it the biggest possible (100X100) size. Otherwise it will be 100X85 or something like that.
The greater the challenge, the more glorious the triumph