On the Imgflip front page it's very misleading where it says "You earn points when your submitted images or comments are upvoted."
That's true -- BUT -- if you look at All-Time Leaders, you'll see folks with DOZENS of featured memes, THOUSANDS of creations, and MILLIONS of points.
The reason is that you ALSO get points for POSTING COMMENTS, even if they are NOT upvoted. I don't recall the values, but the number of points for an "Add Meme" comment is MUCH higher than just a TEXT comment.
ON YOUR OWN memes, you get a few points for YOUR FIRST text comment. No points for subsequent text comments. I don't know if you get points EACH TIME for text comments on other folks' memes.
As mentioned, Add Meme comments get higher points. That's why you'll see some folks post Add Meme "comments" all over the place with one or two words, e.g., "Good one!" or "Ha!"
Related to that, a lot of folks, if someone upvotes one of THEIR memes, they will click on that user's name and go through that person's memes and upvote some (or even ALL) of THOSE.
And, yes, there ARE users who simply upvote loads of memes, knowing that SOME of the folks they do ONE upvote for will upvote a BUNCH of THEIR memes.