For me, a passive upload would be something like Dropbox. Stick it in there and forget about it... turn your computer off and it'll start automatically where it left off when you fire it up again.
Seeing that's not something that Shutterstock offers as far as I'm aware, I'm assuming he might be on about a passive income? If that's the case then pretty much every site operates that way. Upload your stuff, forget about it, watch the payments roll in.
Or you're on about something completely different! A bit of clarification would be nice!