Hello there,
I've seen this question come up about 3 or 4 times in the past 10 years. That seems infrequent, but i think that is because most people just assume that it cant be done so they dont even ask. But then again, it has come up, and i have thought about it a little myself because i had many hand drawings of circuits from the past that would be nice to have converted into pure digital format, complete with neat and tidy symbols for all the components like resistors and capacitors and transistors.
There are two direct ways to do this that i know of, if you dont need it to be in a perfectly neat form like a drawing that originated in software such as in LT Spice.
The first is to scan it with a fast scanner. This creates a drawing that is exactly like the hand drawing.
The second is to use a high resolution camera. I recommend at least 10 Megapixels. You take a snapshot, store in in some directory.
Of course these techniques are not ideal either. We get a drawing that is just as sloppy as the original. To get it into a really nice and neat form however brings in some problems.
First, not everyone draws symbols the same. Some draw inductors that look like resistors, and some draw caps differently.
Second, the drawing would have to be scanned or photographed first anyway. Once this is done however there may be a way to convert it into a really neat professionally drawn schematic.
The question that comes to my mind though is, just how much would we need this? If it was an everyday thing it would be worth it to come up with some software piece that could interpret the drawing and arrange everything into a neatly drawn schematic. I am of course talking about fairly sloppy hand drawings not professionally drafted pencil drawn schematics that already have a neat and orderly form. There would not be much to a program that can convert the latter into a minimum byte count file with a neat line drawing. The sloppy drawings would be hard to convert because the components can be all over the place, with connecting lines looping over and under things here and there and everywhere. There would have to be some software/human interaction i would guess.
It would be an interesting program to write. For drawings that are already neat it would be a snap, but for the sloppy drawings very difficult. I have to wonder if anyone has made this kind of software yet.
For my own purposes i have found that if the drawing is scanned or photographed and tehn converted into a .gif file, it doesnt take up a significant number of bytes. Yes it's not any better looking than the original unless i edit it by hand later. Sometimes a few little edits however and the drawing looks much better.