Original game case covers can be purchased and then resold to others, under the First Sale Doctrine. Making copies of original game case covers for sale to others, however, is not
clearly "fair use." A lot can depend on the image, the image resolution, the use made of the image, the effect of the use on the market for the game, and, perhaps most importantly, the litigiousness of the copyright/trademark holder.
Here is a link to Andy Baio's Waxy.Org site and his tale from 2011 of the pixel art image he created from an original album cover. The artwork Baio created for use on his own album cover became a costly lesson for him on the limits of "fair use." He wound up settling with copyright holder Jay Maisel for $32,500 (
http://waxy.org/2011/06/kind_of_screwed/). Baio's use of Maisel's photographic image to create his own artwork ran into copyright problems for several reasons. One reason was because Baio created his work for a commercial project.
Screen shots of images taken from video games have led to lawsuits in the past, as well. For one case to review, you can look at
Sony Computer Entertainment America v. Bleem (
https://www.law.cornell.edu/copyright/cases/Sony_v_Bleem.htm). The
Sony court found that the use of screen shots, at least for comparison advertising purposes, was a fair use of copyrighted material. It cost a lot of money for both Sony and Bleem to get to the point of a court issuing an opinion, though.
There are several factors a court considers when determining if a use is a fair and an excusable infringement, or a not-fair and a costly infringement. Both the Baio site and the
Sony case discuss fair use in enough depth that you can see what is looked at by a court when deciding a case where "fair use" is used as a defense.
I read over The Cover Project's website and it appears that the site's forum has talked about copyright infringement and how copying the images could stretch the limits of fair use. It also had a discussion on stores that will not print out the images. The stores that refuse to make prints of copyrighted works are smart because they can be held liable for contributory infringement (
Basic Books v. Kinko's GraphicsS.D.N.Y. 1991:
http://www.bc.edu/bc_org/avp/cas/comm/free_speech/basicbooks.html).
Because I am not entirely certain how The Cover Project operates (ie, if they are licensed to sell game covers), I will only say that you would probably be smart to confine any printing of game covers to your home printer and your use of the game cover images to personal game-covering ones.