Improve your web site’s comment section by only allowing unique comments! Now every meme image will need to be one pixel different in order to be reposted. The Internet is saved!
Moderating the comments section of any web site is a thankless and un-ending task. But what if there were some way to make it slightly easier?
Instead of just allowing any comments, we can require that comments be totally unique and never-before-seen.
Once a comment is made, or an image is posted, a “fingerprint”  of that data is saved, and that exact comment can never be posted again (UI implementation shown in Figure 1).
 For example, an MD5 sum.
This will automatically get rid of many types of classic low-signal posts (e.g. the historical but rarely-seen-noawadays “First post”) and reposted memes. (This may or may not be desirable, depending on the type of site being run, of course.)
Observation about images:
Since images must be unique to be reposted, the easiest way to re-post a meme image would be to make a small change to it and re-save it (or make no change at all, but re-save it using a lossy compression method). For a lossy image format like JPEG, this would lead to an interesting situation in which memes became more and more corrupted-looking as they are modified and re-posted over and over. This would even allow the lineage of a meme to be traced by looking at its variously-compressed versions.
PROS: May discourage certain low-effort posts that you’d want to moderate away anyway, saving moderator time and improving web site quality.
CONS: If a 32-digit hexadecimal number is used as the output of the “fingerprinting” hash function, then only a maximum of 16**32 comments can ever be made to your web site. If your web site gets 1 million unique posts per year, then some time in the year 340,282,366,920,938,448,064,954,991,902,720 A.D., all of the hash values will be used up, and people will no longer be able to post on your web site. Also, your visitor counter will probably have overflowed by then!