You know if you just add an alpha layer after you can crop out the white.
Then go back with a soft eraser and just get rid of the rest of the white left behind.
If you're using Gimp then you click on the layer displayed at the side and it will have an option if you right click it to "add Alpha channel".
Look towards the bottom and you'll see the option.
Last edited by Kohta; Apr 2, 2016 at 10:53 AM.