Rotoscoping in flash is much more time effective if you don't trace every frame. What makes rotoscoping in flash easier is using movieclips for the major sections and animating these sections. Basically, you do one generic trace for a section of the film that is basically constant in perspective. Then you seperate the sections with movement into thier own movieclips, adding tweening where necessary. Similarly you can import photos and trace them into sections for animation. 747 animation using photo tracing technique described