Just Google "marijuana vector" or "marijuana png" and use a vector image of a marijuana leaf as a mask. You could even throw on the Big Wave effect on the mask to make it look trippy. This is a cool clip to use with png masks in Resolume:
http://vimeo.com/channels/beeple/9382269 Just change the color to green in Resolume when you're using it with that mask.
Also I dunno if you know but there are plenty of movies out there that feature people smoking marijuana in them, comedies like Bongwater, Evil Bong, Cheech And Chong, the Friday Trilogy, Grandmas Boy, Half Baked, Harold and Kumar Movies, How High, Humboldt County, Lammbock, Pineapple Express, Reefer Madness (Musical and the original), Rolling Kansas (I dunno if there's any marijuana in this movie, I feel asleep watching it in the first 10-15 minutes of the movie).
And there's also documentaries like The Union The Business Behind Getting High, Acapulco Gold (The one from 1973), The Fire Baptism and the Lost Sacraments, Grass by Ron Mann, High: The True Tale Of American Marijuana, In Pot We Trust, Marijuana INC CNBC, National Geographic "Marijuana Nation", Super High Me, Timeshift - The Cannabis Years.
High Times also did two DVDs of their Cannabis Cup event in Amsterdam, the 2003 version is longer, it has a lot more footage of weed strains and bands like Fishbone playing music than the 2008 documentary. There's also a lot of comedy segments and a Survivor parody. The one done in 2008 is the 20th anniversary of the Cannabis Cup and it's the better of the two if you're going to watch one of those things. I think the DVDs might have a High Times watermark on them so you might want to crop those out or zoom in on the video in Resolume.
