The only votes that are counted are the votes cast for random pictures displayed on the front page. So if you want to manipulate the voting for your own photo, you'd have to load the front page hundreds of thousands of times waiting for your own picture to come up repeatedly, which is hard to do without being detected.
To enable an algorithm like this on Digg and reddit, the sites could present users with a sidebar box that displays random stories from the pool of recent submissions. (reddit already has a serendipity feature that users can use to select a random story from the available pool, which could be leveraged for this purpose.) Once a story has collected, say, 100 votes -- or whatever number is considered sufficient to provide a representative random sample of how the story appeals to people -- then on that basis the story can either be buried or promoted to the top, where it would be seen by, say, 100,000 people
I won't waste my breath saying how it's unfortunate that this is necessary. I like being able to vote for a specific story. But the current way doesn't work, it's popularity approach which is easily gamed.
The random sampling is an interesting notion, though I am afraid the sample will be so limited that the results will be suspect. Yet how would you tell? One article is mostly interesting as another, as long as it's not blatant puffery.