Using The GIMP🔗
The Gnu Image Manipulation Program ("The GIMP") is a superb tool for creating image files used in games. I find the following plugins useful:
SpriteSheet.scm -- Generate a sprite sheet (for animated sprites) from a set of layers.
Crazy uses of GIMP🔗
Some of the ways I use GIMP are, admittedly, a little crazy. If you're crazy too, you may find these useful. :P
Picking colors from anywhere🔗
Sometimes I want to pick colors from anything I can see on my screen, or in life. While there are programs, such as Gpick, that can make this easier, I often fall back to GIMP, since this method works on any platform, and even with digital photos I take on my phone or camera:
Take a screenshot or photo using whatever native mechanism your platform supports (this works on mobile phones, tablets, too!).
Open the file in GIMP.
Use GIMP's Color Picker Tool to pick a color from the image.
Tip
You can use magnification to zoom in on any portion of the image to make it easier to pick from.
Done. I know, this seems so obvious now, huh?