The guidelines are only for pics that are uploaded to the site (like...physically). The reason we have to police sig images is because if you host it, the site does not recognize the size.
I think, for this contest, the 2kb limit should not apply.
Remember: The only way you get a board message on size for images is if you try to directly upload them to the site by browsing your local computer.
Almost no one does it that way anymore.
This also does not apply to the Gallery. Its just an old vBulletin rule to make sure board space is saved.