I don't know... There's been several times I did a Google Image search for "meme [keywords in my intended meme text]" and found that the meme had been done before, usually within the first two lines of images (I use a laptop), so I didn't do it. Didn't take long at all.
One time, I saw one with literally dozens of the exact same text, but all different backgrounds, it'd been reposted so much. Somebody had to be the first, the clever and creative originator, but that person's identity is lost in the ether...
I'm full-blown obsessive-compulsive (not just someone with a quirk), so I acknowledge I may be going too far with this. I have only once resubmitted a meme, and felt so much like I was cheating (if my memes aren't good enough to get upvotes, that's that) that I never did it again. Stupid, illogical, I know. Reprogramming my brain is not an easy task. I've got it around to thinking it will be okay to resubmit once the meme is a year old (started on Imgflip November 30).
I didn't become a repost nazi until someone reposted one of my memes (not just a paraphrase, but the exact background and text, on another meme site) and tried to pass it off as their own. I thought that was extremely disrespectful to me.
Again, with the obsessive-compulsive brain reprogramming, I've gotten myself to the point that I won't point out the reposts of others' memes, but I still can't just let the reposts of MY memes go untrolled. If this still makes me a repost whiner, so be it.