You should get the old fashion two-color red/cyan color like Maggie is wearing. They cost 98 cents at Toys-R-Us.
Do not get the modern glasses they have in movie theaters or for TV today. I don't see any background pictures on internet for these. I got a free pair at the movie house and they no good on internet pictures. They also sell these free ones at Walmart for $19.95. But they don't work.
From internet I have bunch of backgrounds for the red/cyan type like Maggie is wearing in above pic. If you want, I'll post about 10 good backgrounds here.