Download and install GIMP for free. Find a simple, cute picture from a free stock image website, such as Stock.xchng. You may have to sign up before you can use any images on some stock image websites. Save the image to the photo library of your computer.
Start GIMP and open the picture you selected by clicking on "Open" under "File." The image will appear on your screen. Select the "Rectangle selection tool" from your toolbox. Click on the image and drag your mouse to create a perfect square on the image.
Navigate to "Crop to Selection" under "Image." This option will trim your image down to a perfect square. You will use this perfect square to create your avatar. Select "Scale Image" under "Image."
Enter "128 pixels" for the "Width" and the "Height" of the image. If your forum or community supports avatars of a different size, you can enter a different value. Click on "Scale" to put the changes into effect.
Use tools, such as the "Curves" and "Level" tool to add special affects to your cute avatar. Once you're done using these optional tools, click on "Save" under "File." Go to the forum or community and upload the avatar.