How to create Roy Lichenstein style Pop Art in GIMP

Learn how to produce Roy Lichenstein style Pop Art from your photographs using GIMP image editing software.
This is based on several Photoshop tutorials, but is 'translated' for the Gimp, which doesn't have the 'new adjustment layers' or 'filters-sketch-halftone' options that the Photoshop tutorials rely on.

Handy shortcut keys:
ctrl+m = Merge all visible layers
[ = brush decrease size
] = brush increase size
p = paintbrush tool
shift+e = eraser tool
o = eye-dropper/colour picker tool

Remember to save your project as an .xcf file as you go along, in case you lose your work.