Quote from the movie Animal Farm: "BUT SOME ANIMALS ARE MORE EQUAL THAN OTHERS"
Using a QR Code in a campaign that is build up with just ordinary black white squires doesn't make it stand out. To a QR Reader app this doesn't matter, it treats every input as equal.
It will try to find the three locator squires, and then read the pattern. Converts the pattern into a data-stream, checks the stream for errors and shows the result. Or reports a fail if too many errors are detected.
In order to make QR Codes more appealing, by a little bending of the rules QR Codes can generate a different appearance.
Here are some examples, that do have the bit-stream error free, the color and element shapes do not comply fully with the contrast rules. It is a fair trade off with the result however..