GovernorSimulus; I'm not quite sure why you'd want to upload JPEG images anyway.
Generally (actually ... almost always) folks upload a (zipped) saved game just before completion of their city, this gives other players more insight into how your city works (they can view the advisors' screens for example).
Anyhoo, it's your choice; I think the accepted limit for a file is, as Gweilo says, 8 MB.
"Can I draw you a beer, Norm?"
"No, I know what they look like. Just pour me one."
Cheers !!