Seriously. If I REALLY wanted to be paranoid, which I'm not:
Consider that this can come in an image file, linked from any web page.
If a government were using something like this as a backdoor it would be very useful. Say you passed a law (CALEA maybe) that forced telecom providers (backbone providers) to allow you to intercept traffic. Part of the specification could allow for a replacement packet/response. You could insert HTML code into a spoofed response that included a link to an infected image.
Something like,
If I see an IP of interest, hold the responding packets (until I'm sure it's complete).
Parse the returning html, and insert an infected logo at the end from one of our servers.
Voila, instant compromised machine.
Wouldn't this be a lovely (deniable) backdoor?
God, the pain medication must be making me REALLY paranoid tonight.