Mouse, they're proper PNGs with transparent background, and they'll work just fine in programs like Photoshop, GIMP, PaintShop Pro, etc.

Here's a quick test in PaintShop Pro X7:
Click image for larger version. 

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Robbie, when I created my Panjo account, I used the exact same username (and password) that I have here at the Guild, with no variations in upper/lowercase letters.