Programatically drawing a perfect circle is not all that difficult. It's based on some very simple math, afterall. You input two parameters (a center and a radius) and output the circle.
But if you don't have tools to help you, drawing a circle freeform (as in holding a pen in your hand) is very difficult! If I wanted to simulate a person trying to draw a circle, is there any algorithm I could use that takes three parameters (a center, a radius, and a "wrongness factor") and uses the magnitude of the third value to create random imperfections in the circle, while still producing something that looks recognizably like a person trying to draw a circle?