How to create Colorkey images with GIMP
Note to myself: 1. File => Open 2. Image => Mode => Grayscale 3. Edit => Copy 4. Edit => Undo 5. Layer => New => Transparency => ok 6. Edit => Paste 7. Layer => Anchor Layer 8. Layer => Mask => Add Layer Mask => White (full opacitiy) => Add 9. Now use [...]