This can be done without any problems
I can do it, but I have to found a good video with one-colour background (a color the girl doesn't have on her, to be able to use transparency) like std said.
I found a video on youtube, grabbed it and try to make the background one-colour but this is a difficult process for some parts...
So here's the deal: if someone can make a good video with a one color background, let's say about 20/30 seconds max (if the video can be looped it's a plus, but not necessary)
I can use the videos provided by deonidis (only the last one, the other links are not avalaible anymore), but it will be better to have our own video(s)
I even asked my girlfriend, but the idea to be famous on xda doesn't seem to be attractive for her lol.
So, anyone, good video for this fun project ?