The iMovie video effect "Edge Work" (found in Quartz Composer) turns your video clip into a black and white ink drawing.
iMovie Video Effects - Edge Work
Effect In, Effect Out:To apply the effect to only part of the video clip, move the sliders to the places/times when you want the effect to begin and end. Leave them both set to 0:00 to apply the effect to the entire clip.
Radius: Move this slider to adjust the size of the black and white sections of the clip. The closer you get to Max the larger each section becomes, making your clip more and more unrecognizable.