This post was created with the intention of providing all the information we have regarding 9gag's policy of reposting and censoring comments. All this information was drawn from posts from this subreddit
Introduction
9Gag is closely controled by the administrators. They steal posts from all around the internet, mostly from reddit, and delete comments/posts at will. Trying to warn 9gaggers about this is useless, they will never see your comments.
Here are some known facts:
Almost 20% of the images found on 9gag were taken from reddit
Most of the images found on 9gag's front page were uploaded by the administrators of the website.
All of the posts made by the administrators were taken from other websites, mainly reddit
All of the posts made by the administrators receive automatic upvotes as soon as they are submitted
Certain words such as "reddit" or "repost" are filtered, and comments/posts that contain them are deleted
Images stolen by 9gag are watermarked with the 9gag logo, even though they were not generated by them
Repost machine
9Gag employs what we call "Repost machine". It is a system that takes popular posts from reddit and reposts them on 9gag. This post by /u/FroggierSnow7 explains it. This used to be a manual process (more about the old system can be read here), but it is currently automated.
The system removes any existing watermark and adapts the title so it is appropriate to 9gag
The Repost Machine is not perfect, and it sometimes reposts images that makes no sense/can't be understood by 9gaggers
Administrators add fake upvotes to posts to create the illusion that there is good original content on 9gag. 300 upvotes are added soon as they post something and some more thousands after some time so it can reach the frontpage.
Reddit is not the only source of their content. They also steal from other websites
(Currently, the username of the original poster is not shown. This means it's impossible to know whether the image was submitted by the administrators or the users)
This post by /u/martinmine shows the number of reposts found on 9gag and from which subreddits they steal content (mainly /r/funny, /r/pics and /r/gaming).
Censorship
A list of words that are automatically removed can be seen in this post, by /u/konfu1. The list includes:
/u/konfu1 was kind enough to create a Greasemonkey script that shows you which comments you made are invisible. You can find it here.
Proof of censorship can be seen in this video by /u/bradleygoddard
Conclusion
9gag administrators are extremely shady. They blend themselves in the community to blatantly steal content from other websites, censor comments to prevent 9gaggers from finding out the truth, promote their agenda through fake upvotes, watermark stolen posts to attract more visitors, manipulate submission times and more.
They are also very stupid. They often post images that only make sense for a redditor, and even though 9gaggers don't understand how an image no one finds funny got to the frontpage, there is nothing they can do about it.
Thank you very much for reading this. Special thanks go to /u/9FAG_EXPERT, /u/martinmine, /u/konfu1, /u/bradleygoddard, /u/thetonyk123, /u/cedriceent and /u/FroggierSnow7