So a code with a high error correction factor can repair a QR code with a logo obliterating the middle of the code.

"Claycode: Stylable and Deformable 2D Scannable Codes"

https://arxiv.org/abs/2505.08666

https://claycode.io/pages/scene_claycode.html

https://www.youtube.com/watch?v=Sx9k2iyXQhY

Basically, at the maximum level of error correction, you can obscure up to 30% of the code (excluding the corner target) and the data is still readable.

However, most QR readers will adjust the colours they see to pure black and white - so light colours will be squashed down to white. That means you can have some pretty colourful designs and still keep the codes readable.

Ideally, the border should be at least 2 blocks wide - but modern scanners are pretty good at picking out the targets.

As for size - that depends on your target audience. If your users are sat down and have the QR in front of them, you can cram in as much data as you like. If the code is on a billboard people are far away from, use as little data as you can and make the code as physically large as possible.

The math we have mastered is incredible. If only they could impart this wonder to children instead of rote worksheets enforced by drill sergeant math teachers.

While I'm ranting, I checked out a book from the library yesterday called "Math with Bad Drawings", it's very fun, and approachable for anyone with no math background, kids and adults enjoy it.

We need more STEM for fun, and not just STEM for money. That's how we get good at STEM.

I've had it happen to my submissions in the past.