Big deal. What about the thousands of forums that allow you to post <img .../> tags?
You're only going to get a few thousand people installing your app, and they are not all going to do it within a few seconds of each other. Your browser is liable to cache most things this 'malicious' app forces your browser to retrieve. And most websites can handle serving a few thousand pictures over the course of a week perhaps. In fact I'd go so far as to say that's what they were designed to do.