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My advice is to contact "memegenerator, knowyourmeme, and others" and ask them what licensing agreements they have with the copyright holders that allow them publish the content. You may be surprised to learn how much or how little money changes hand.

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I spoke with the founder/owner of campusmemes.com asking the same questions. He basically said, "We operate business as usual until we get a C&D. Remove the image. Life goes on."

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Hmm, The Monetization of Copyrighted Content without any Licenses sounds more like a service than a software product. Maybe try to obtain license agreements from the copyright holders and put the funding for agree'ed to licenses in the Kickstarter campaign.