Quick Response Codes are appearing everywhere. You can see them in museums, near the tourist attractions or all over the web. There is no doubt that QR Codes are useful as they can contain any information within reasonable limits.
The best place to start is to read the Wikipedia entry about QR Codes as it contains all the needed information about standard.
To generate your own QR Codes you need to install qrencode utility:
$ sudo apt-get install qrencode
You can easily encode short text like URL:
$ qrencode -o qr_blog.png "http://blog.sleeplessbeastie.eu"
$ qrencode -o qr_sms.png "smsto:+48111222333:sms message"
File contents (vCard in this example):
$ cat vCard.vcf BEGIN:VCARD N:Galazka;Milosz;;; URL:http://www.sleeplessbeastie.eu END:VCARD
$ cat vCard.vcf | qrencode -o qr_vcard.png
Text from standard input:
$ qrencode -o qr_text.png If you are insecure, guess what? The rest of the world is, too. Do not overestimate the competition and underestimate yourself. You are better than you think. Timothy Ferriss ^D
By default each dot is 3 pixels in size, you can increase it by using the -s parameter:
$ qrencode -o qr_bigger.png -s 12 "This QR Code is big"
You can add a little blur using ImageMagick convert command-line tool:
$ qrencode -o - "http://blog.sleeplessbeastie.eu" | \ convert - -blur 0x.5 qr_blog_blurred.png