Making backgrounds of animated GIF files transparent

From: http://graphicdesign.stackexchange.com/questions/39772/making-backgrounds-of-animated-gif-files-transparent

Download: https://eternallybored.org/misc/gifsicle/

Code:
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gifsicle -U --disposal=previous --transparent="#ffffff" -O2 anim.gif > anim_trans.gif 

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