I'm really sorry if somoene of you does not appreciate Zell's "art". I must admit that, even though I like the accuracy of his artwork, the subject is often too cruel and graphic for me too.
In general I don't like pictures representing people being mutilated or dismembered. I prefer a lighter degree of cruelty. Zell' series "Cold, cruel vengeance" deals with a really cruel kind of vengeance, ending with a terrible and extremely painful death of the victim. Everything is described with very graphic details.
Most likely, in many medieval dungeons some unfortunate people really experienced such form of cruelty.