ELI5 QR Codes - how do they work even with portions covered or obscured?

How are QR Codes better than regular barcodes? How do they work? The fourth corner square is kinda important - what kind of processing is going on for a QR code to be decoded? Why is error correction so important in QR codes? ... we explain like I'm five Thank you to the r/explainlikeimfive community and in particular the following users whose questions and comments formed the basis of this discussion: puppett_master, berael, middlefingerin, jagedmetalos, superpansy, simbonegtp and jcdu To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Join us on Twitter: https://www.twitter.com/eli5ThePodcast/ or send us an e-mail: [email protected]