Collectible Card Game Headquarters

I have downloaded some custom decks and some cards have no images. How do I go about fixing that? I assume I can add the images myself. If so, where's the best place to get the images, and how do I add it?

The various DLC available here usually includes a .WAD file that contains all the art for that specific mod. Be sure to check the opening post of the threads thoroughly. You may have overlook the link. Also, you can just post a reply in that particular thread.