They do take a lot of time and patience to retouch - at least mine did, because in the results of the scanned sketches, the pencil shading and lines weren’t consistent - some were dark and splotchy and not nearly as smoothly blended as the original. Here’s another odd thing: I am left-handed and cannot draw nor even write my name where you can read it with my right hand - yet, I have never been able to use my mouse with my LEFT hand, thus I do every bit of detail with my right hand. :)
One of the problems that I have with this sketch of my wife is that there is no photograph to use as a guide for shadows and shading. The only guide is the badly smudged original. So I not only have the problems generated by scanning but a bad original as well. I should have taken better care of it. Don’t know if I’ll ever be able to do anything with it now.
So, you draw with a mouse? I have one of the drawing pads that attaches thru a USB port but it doesn’t help that much. I use a mouse for cartoons but then they are crude with no shading.