You can only do this on Windows:
Start up your DVD. When the part you want as your avatar is playing, press
Print screenSysRq
The button is located near F12. Go a little right, and you've found it.
Now, exit your DVD, and go to Paint. Press Ctrl+V. The image should appear. When the system asks you if you want to save the image, click yes. When you've done what you've wanted to do, (name,
MAKE SURE YOUR FILE TYPE IS JPG ) click Save. It should appear in your My Pictures folder. Go to get your image hosted, (if you don't have one get a free one
here) and host your image. Find the URL of the image, press Ctrl+C. Go to your control panel, select avatar settings, and go to the place where you can select your avatar at URL. Press Ctrl+V.