QR codes - same URL - different image - why?

Question

Why do some QR codes look different when using the same URL?

Answer 1

There are 40 Versions (sizes) of QR Codes, 4 error correction levels and 8 masking possibilities giving a total of 1280 possible QR codes for any given input.

Typically the version is chosen based on the amount of data to be stored and the mask is chosen to produce the best image in terms of readability. The error correction level is chosen by the encoder based on how much data might need to be recovered...

Answer 2

Choosing a different error correction level will result in a different image. The higher the level, better the chances it can recover from unreadable data.

http://en.wikipedia.org/wiki/QR_code#Storage