Now explain to me, how would that work given the gameplay mechanics, design choices and engine restrictions?
Upload a picture to Photobucket. Now find it, click edit, and select "Effects", then "Cartoon", "Sketch" or "Colour Sketch". The website then automatically re-renders the image with your desired effect. Now, same principle. Your 'painter' companion, or however this system would work, could save a snapshot from their point of view, so it'd just be a screenshot taken by the NPC. The screenshot would then be rendered as a coloured cartoon, and saved as a picture file. Done. It's a little unwieldy a process, but probably possible.
Also a lot of work, for a pretty small result, but eh. Personalisation is personalisation I guess.