Hi everyone,
Jean-Frédéric https://commons.wikimedia.org/wiki/User:Jean-Fr%C3%A9d%C3%A9ric has made an upload campaign on Wikimedia Commons for the event: https://commons.wikimedia.org/wiki/Campaign:Wikimania
Uploading from this link will put your pictures in the good category automatically. No one is forced to use it, but I guess it might be useful for some people.