Amassment Message Board

Well, a doujinshi is fan art, so you'd have to ask the artist if you can use their art for your layout - that's not really about any policy, just because the art is theirs and it's up to them to decide where do they want it to be used.

An analogy involving the public use of images from games, movies, etc. doesn't work in this case because those are original works. That's a different discussion involving distribution of content by large companies and fair use laws. Legal usage of those images have nothing to do with whether or not you have purchased the product.

Permission for usage, manipulation, and/or reposting of fan-created works not belonging to you is based on proper etiquette in the fan community, which we are part of.