Keep in mind, because the image involves an http get request, the host of said transparent dot can also dump a cookie on you; this is how a lot of advertising a

Keep in mind, because the image involves an http get request, the host of said transparent dot can also dump a cookie on you; this is how a lot of advertising agencies track conversions for cost-per-action ads. They tend to drop them for cost-per-click ads too, just to be extra annoying :)