Last summer I had an inkling of an idea that used basically the same strategy. My idea (never implemented) was to set the background images on visited anchors to a dynamic image url that could be used to track pageviews from other sites, to perhaps determine what links from your site your visitors found most interesting, even if they didn't click to them from your site.
There are plenty of terrible use cases for something like this, but also plenty of benign and probably useful cases as well. If you were a search engine, for example, you could determine if a user has been to sites that show up in the search results, even if they don't click on the links from your site.
Last summer I had an inkling of an idea that used basically the same strategy. My idea (never implemented) was to set the background images on visited anchors to a dynamic image url that could be used to track pageviews from other sites, to perhaps determine what links from your site your visitors found most interesting, even if they didn't click to them from your site.
There are plenty of terrible use cases for something like this, but also plenty of benign and probably useful cases as well. If you were a search engine, for example, you could determine if a user has been to sites that show up in the search results, even if they don't click on the links from your site.
The full write-up of my strategy is here: http://tinyurl.com/6fnjod