> I will note that I have not yet tested this pass in a real library yet
I get this project was mostly for fun, but why not spend the 10 minutes it takes to test the final solution before sharing your work?
So even if you, the human, can read it doesnt mean the device that authorizes you can.
Loyalty cards at retailers come to mind, for example. POS systems often support scanning coupons from phone screens.
Whether that barcode can then actually be read by a specific reader from a phone or not is arguably a different concern: Some readers support it; others don't. Obviously a passbook version of a paper barcode is useless for the latter.
Personally, I found the post valuable regardless of whether the barcode would actually end up working at the author's library or not; I have a few scenarios myself where I know screen-presented codes are accepted.