hmm, I have never used that software, so I cant help specifically. But you are limited to what you can do, especially if you need the final image to be a certain size. if the final size doesnt matter, you would just select the 'picture' area, then crop. eg
I guess thats obvious. So, im asusming you need the image to stay a certain size? In that case, i think you are limited. You are going to distort the image if crop it, but keep the side measurements the same - ie it will be stretched in one direction or another.
eg
the only other thing you can do is 'fill' the offending white area. Thats what I did to make Lynnie's avatar - her images were very different sizes, so on some of them I copied the background and 'painted' it over the blank areas. but I use photoshop, which is very sophisticated for this kind of work...I really know nothing about your software, sorry.
Here is an example of what I mean......
