The above image was made with
(which is also available as Debian package).
It's a 21x21 'alphanumeric' QR code which contains the text 'HTTP://SPUT.NL/'
and has error correction level 'Q'.
Using upper case only can reduce the amount of data, as can be seen below;
The webbrowser converts 'HTTP' into 'http', hostnames are case insensitive
and my webserver redirects 'sput.nl' to 'www.sput.nl'. Not all QR readers
support upper case URLs, but most do. If your QR reader doesn't understand
the left QR try the other ones.
Files and paths are case sensitive though. So HTTP://EXAMPLE.COM/FOO/BAR and HTTP://EXAMPLE.COM/foo/bar are not the same thing!