Which software was used to make the "Iron Ballmer" GIF?

You know, this one:

Ironballmer_medium

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I have done a lot of work in Adobe Flash, but unfortunately flash is a pain to work with importing but most importantly exporting videos. Photoshop seems like it could be used (http://disneyfaceswap.tumblr.com/post/19619744791/making-a-face-swapped-gif) but still it doesnt seem like it was made for this kind of editing. I'd like to know if there's any software specialized in stuff like this, one that can easily import videos, import and drag bitmaps as well as export high quality videos and gifs.

So I guess what I'm trying to say is: If you were trying to make something like this gif, which software would you use???