Doubly damning is that the post is a fake, at least in the context everyone thinks it's in. It's a screenshot from a porn movie, not a random picture.
(Thinking out loud, just skip the rest of this.)
Posts like that do attract fourteen year olds, and once you do you can never, ever get rid of them. It's self-reinforcing.. Fourteen year olds attract other fourteen year olds, who create submissions like the one above, which attracts more fourteen year olds. One way to fight it is to implement a harsh banning system, the way Facepunch Studios did. Check out their ban list: http://forums.facepunchstudios.com/showbans.php ... I count 93 bans today alone. Most for a week or longer, complete with reasons and viewable to the public.
And yet, a brute-force approach like that only sorta works. What's needed are strong community values combined with a strong punishment system. But not so much as to stifle conversation innovation - just enough to filter the noise.
Karma works, but some people need to be made more equal than others in that case; someone that's been with a community from the beginning is a hundred times as valuable than a newcomer (not an exaggeration), because they help enforce community values. It follows that they should get a karma vote weight proportional to their contributions. This means karma points with a decimal value instead of an integer.
To decide how much vote weight someone gets, you could use a simple factor like 10% of total karma. But much more interesting would be: If you upvote foo's comment, you boost foo's vote weight by 5% of your vote weight. If you downvote their comment in the future, that 5% becomes negative to their vote weight. What that does is ensure that at any given instant, foo only has as much power as he should have. Time with the community only gives foo a small power bonus, since his power is mostly determined by current public perception. And it forces people to really back up what they say. If they say something horrible, they may be rendered powerless tomorrow.
If everyone's karma starts at zero, and everyone's contributing 5% of it, then how does anyone gain karma? Ahh, well.. That's where being with the community from the beginning plays a part. For each day you make a comment that is upvoted, you get one karma point which can never be taken away.
If you're a part of something small, you feel like you're a part of something special. So one way to fight noise is to stay small, or divide your community into sub-communities (almost imopssible).
But I think most important is a goal, the kind Startup News has (you better be submitting stuff related to startups). With a community goal, it's at least an order of magnitude easier to filter out the noise.