1. Save the picture you want to use on your desktop.
2. Open the picture in Gimp and export it as Avatar.jpg.
3. Go to your desktop and rename the file .face and make sure to remove .jpg.
4. Open fie manager.
5. Go to your desktop folder and press ctrl+H.
6. Find .face and cut it to your user folder located in home.
7. Restart your computer and you should see the new profile picture.
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