http://en.wikipedia.org/wiki/Rotoscope

its rotoscoping. a very common animation trick, and since naruto is like all anime is a show that airs every week when animations typically take months to make, i dont blame them for using it. im sure that it wasnt, but the proper steps where taken to roto the footage legally. mizuchi was pointed out that the key animators where the same for both productions, but not only that its even possible that the original bebop footage was probably rotoed off of live action footage, studios including classic deisney did it all the time. its no different then the motion capture thats used in 3d animation today.