Trade show photos & model releases

I am getting ready to put in a quote to shoot a trade show. The photos will be used in international brochures and on the web over to advertise next year's show.

My main concern is the logistics (or near impossibility) of obtaining model releases from everyone in the photos selected for use (large crowd shots with recognizable faces, etc, etc). I assume that model releases would be required since the photos will be used in advertising, but I may not be correct on this.

I think maybe the easiest way to obtain model releases would be to make it a condition of registration. However, the registration has already begun for the show and there is no wording in the registration forms on having the participants agree to use their likeness in advertising the show.

My question is would it be enough to place a clause in my contract with the show management that gives them the responsibility and liability regarding the model releases or would I still be liable as the photographer? Are model releases required for this type of photo use?

This is such a big issue that I'm considering not even bidding on the show due to the potential liability.

Thanks for any help and advice.

I've been to trade shows where there's a notification (usually a sign by the door) which essentially lets attendees know that the event is being photographed, and that, by virtue of being in the venue, they consent to their picture being used for advertising, etc.

I don't know the exact legalities of the whole thing, but it might be worth a call to the hosting organization...