Step 1: Buying Mini-DVD Cases
Step 2: Downloading the Template
All you have to do now is to download the basic template from above for Paint.net and create whichever front/back cover you want. Do not forget to put the title or logo of the game on the spine!
Step 3: Create your own Cover
In case you don't find anything to your satisfaction, don't worry, there are other ways of obtaining Game Covers (Flickr, Google Images).
Another possible option is if you happen to own a scanner. That way just scan the cover and resize it to match the template.
Step 4: Print the Cover on Paper or Photographic Paper
I therefor printed my Covers on Photographic Paper, which happens to work better for me.
Again, print size of the cover was 17,78 x 11,9 cm on my printer.