at least one poster on this jetphotos (http://forums.jetphotos.net/showthread.php?t=55779&page=94) aviation safety forum thread is skeptical that it's from a 777.
http://www.airliners.net/aviation-forums/general_aviation/re...
In general, airline parts come with serial numbers and other means of identification. It's best to wait a day or two until the origin of the part is ascertained.
http://i.imgur.com/OAw6AOc.jpg http://i.imgur.com/Ti09xEh.jpg
On the other hand, it's pretty rare for large aircraft (or large parts thereof) to go missing, so there aren't a whole lot of places from which this piece of wing could have come.