Guess what? This is copyright infringement. I'm reporting all of your (de)motivational posters. They will probably be taken down until you can get permission from the original artist to use the art. I doubt you will get permission though, knowing how popular it is. It might take about a month depending on how busy the admins are, but it will be taken down.
I didn't say I'll be reporting all of the demotivational on deviantART- just that persons. When someone comes to me and asks me to report something I do it- like hell I care about everyone else who can't post their own art.