Rotoscope
Photoshop's or Photostyler magic wand function works very well. I am
doing a stop motion video in which I have to replace the background.
I only wish this programs implemented a "batch" or script mode like
DeBabelizer to make it easy for us animators to deal with this type
of problem. A related problem is this. I have hundreds of frames
(already rendered and or video captured) in which a color or 2 need
adjustment throughout (batch mode please!). The workaround is to
change one file lowering the saturation or whatever, then creating a
paletted file, then using Alchemy and -f(forcing the palette) of all
frames to that particular file.