You thought of everything.

I dont know how they did it, but they did it. They have everything you need to make a good transparent image, you can even undo/redo/restore if you mess up. Learn how to do it and you can do amazing things. I turned a crosshair transformer poster on my wall into a transparent beauty. It has NO ADS that block the screen. The creator also though of this concept: "I wanna get rid of all blue, but one is dark blue and the other is light", so w/ the aim you hit one color and lets say you hit dark blue and its in the inside. Then the light blue will be on the outside and your able to clean up the rest with an aimed eraser.

Geobot200 about Background Eraser: Bg Remover+