Steam's recent beta allows people to finally customize the images for games in the grid view. Normally NS1 shows up as an icon in the grid view but now people can easily add an image to replace the small icon that has always been there for unofficial steam games. And for some odd reason my ns2 image never updated so I quickly edited some images for that as well.
All credit for the artwork goes to UnknownWorlds, specifically Cory. I just simply made them fit and added some logos.
To Download: http://imgur.com/a/ry3Fy You can download them from the album above by hovering over the image and clicking on the download icon.
To use: You need to be in the current Steam Beta. Go into grid view for your games list and right click then click 'set custom image' Find your image and you're set.
To create: If you're able to make your own. You should make them at 460x215 and jpg works the best.