This is, as they say, a non-trivial task.
For example, we can attempt to detect and remove craquelure from Mona Lisa’s left eye.
To do this, I had to made assumptions about which marks are caused by craquelure. This was fairly easy for the dark marks, and not so easy for the light marks.
I don’t have anywhere near enough technical knowledge of pigments and how they age to attempt a “colours as originally painted” version. But we can have fun trying:
