Picture help!
You have to crop the original to an 1x1 (square) aspect ratio. How to do that depends on what software you use to edit your images. But generally when you go to crop a photo there is an option for what type of rectangle you want to use, if all else fails you can estimate a square as you select the area to crop, even if it isn't perfect any stretching that OH does to make your avatar fit in the square shape that avatars automatically show in will be minimal and you shouldn't notice it. Hope this helps, if you still can't get it let me know and I will do it for you, it only takes about a minute to do.