To install any of these packs, you can simply use the new Launchbox Image Pack Importer by clicking Menu > Tools > Image Packs > Import. The only thing that's been done to modify these screenshots is that they were all scaled to a height of 720px while maintaining their original aspect ratio to maintain a baseline of quality and uniform size among all images. This pack's initial release contains 3,912 images. Again, many of these are not found in the LB media downloads, and were sourced from a Google Image search. I prefer to have at least a couple screenshots for each of my PC games, so as I would look for the box art to use, I would also download several gameplay screenshots.
This is the 'raw' version of my Uniform Matte Finish and Microsoft Operating Systems packs. I've been manually adding my own media to my LB library for over a year for things that aren't in either of the databases, so there's a ton of stuff here that isn't currently available through the LB Media Downloads. The artwork itself was sourced from around the internet, either through LB, EmuMovies, or a good ol' fashioned Google Image Search. Each of these images has been adjusted manually - great care was taken to preserve the aspect ratio of the source material, and resized to within a few pixels of 546x747 while maintaining as much of the original artwork as possible.