There's definitely a tradeoff somewhere between fanciness and scan-ability though. Say we instead use a transparent mask, so there's both a discernable image in the back and a QR that gets reliably thresholded into the original.

I think it's just a common game to try to use a thing for something other than its intended purpose, especially if that thing can hold an image (QR codes, favicons, etc), because it makes the trick all the more impressive.

How much longer? On the order of seconds or milliseconds?