Rotoscope was an animation technique developed by Max Fleischer in 1917. He patented a device that projected live action film onto the animator's canvas frame by frame, enabling the images to be traced. This resulted in very lifelike animation.
So what has this got to do with Spaghetti Westerns? Well, the rotoscope technique was used for numerous spaghetti western title sequences, usually as simple silhouettes - very 60's, very cool, and very effective. The most famous use of rotoscope in a Spaghetti Western is without doubt the credit sequence of 'A Fistful of Dollars'.
And, hell ... I just kinda like it.