A short guide on using GIMP to create the avatar images.
- Make sure that your layer has an “alpha channel”:
Layer → Transparency → Add alpha channel
If it’s grayed out it means you already have one
- Create a circular selection with the “Ellipse select tool”. Use the
“Tool options” dialog to set the ratio to 1:1:
Windows → Dockable dialogs → Tool options
Once you have the required selection, invert the selection so that everything except your circle is selected, and delete. You should have your central circle left, surrounded by a checkerboard pattern. This checkerboard is not part of the image, it just indicates the transparent parts of the image.
- Crop the image:
Image → Crop to content
Rescale the cropped image to 128x128 at 600dpi.
- Export the image to a format that supports transparency, like PNG