This is new for Gmail but it pretty much screws you over for tracking an email campaign in Gmail. Google now caches images in emails and displays the cached versions to users (the URL you're seeing is to a Google caching server). This means that you will likely receive only one and exactly one request for each image in each email you send since Gmail will have to make a request to your server for the initial caching.
But to be honest you couldn't count on Gmail for accurate campaign tracking anyway since they moved to the "smart inbox" system that is supposed to automatically prioritize your inbox. I'm not sure what else Google has done to anger email marketers but the ones I work with really don't like Gmail.