Hey, thanks for the feedback! I'd quite like to expand this just a bit more for an after-Jam version and I really like the materials idea (perhaps it could feed into a more interactive forging part of the game).
Also, I tried to leave the blueprint blank to see what would happen
Good job with bug finding too. I'd seen the first one in development but hadn't put in time to check for that case or provide a sensible way to show the player - I figured the visible NaN was a division-by-zero error - and yes, it turns out the restriction on only counting areas that have a sketch in either the reference or the players drawing (to make scoring make more sense) leaves you with scoring out of zero for an empty player sketch.
I then tried to do the opposite (because, again, why not?)
Great QA thinking! I hadn't even tried the opposite myself (didn't have the patience to fill in the canvas without some kind of fill tool) and the result makes sense for this. The character getting replaced is a known mismatch between how the sketch area and sprite versions are positioned so they get end up covered by the sprite sized sketch in some directions. I'd seen the overlap but it's more obvious with a completely filled sketch.