The easiest way to generate QR codes with PHP is the phpqrcode library.

The phpqrcode library is really fast to configure and the API documentation is easy to understand.

In addition to abaumg's answer I have attached 2 examples in PHP fromhttp://phpqrcode.sourceforge.net/examples/index.php

1. QR code encoder

first include the library from your local path

include('../qrlib.php');

then to output the image directly as PNG stream do for example:

QRcode::png('your texte here...');

to save the result locally as a PNG image:

$tempDir = EXAMPLE_TMP_SERVERPATH;

$codeContents = 'your message here...';

$fileName = 'qrcode_name.png';

$pngAbsoluteFilePath = $tempDir.$fileName;
$urlRelativeFilePath = EXAMPLE_TMP_URLRELPATH.$fileName;

QRcode::png($codeContents, $pngAbsoluteFilePath); 

2. QR code decoder

See also the zxing decoder:

http://zxing.org/w/decode.jspx

Pretty useful to check the output.

3. List of Data format

A list of data format you can use in your QR code according to the data type :

• Website URL: http://stackoverflow.com (including the protocole http://)
• email address: mailto:name@example.com
• Telephone Number: +16365553344 (including country code)
• SMS Message: smsto:number:message
• MMS Message: mms:number:subject
• YouTube Video: youtube://ID (may work on iPhone, not standardized)

more data type on http://blog.thenetimpact.com/2011/07/decoding-qr-codes-how-to-format-data-for-qr-code-generators/

I have been using google qrcode api for sometime, but I didn't quite like this because it requires me to be on the Internet to access the generated image.

I did a little comand-line research and found out that linux has a command line tool qrencode for generating qr-codes.

I wrote this little script. And the good part is that the generated image is less than 1KB in size. Well the supplied data is simply a url.

$url = ($_SERVER['HTTPS'] ? "https://" : "http://").$_SERVER['HTTP_HOST'].'/profile.php?id='.$_GET['pid'];
$img = shell_exec("qrencode --output=- -m=1 $url");

$imgData = "data:image/png;base64,".base64_encode($img);

Then in the html I load the image:

<img class="emrQRCode" src="<?=$imgData ?>" />

You just need to have installed it. [most imaging apps on linux would have installed it under the hood without you realizing.

I know the question is how to generate QR codes using PHP, but for others who are looking for a way to generate codes for websites doing this in pure javascript is a good way to do it. The jquery-qrcodejquery plugin does it well.

qrcode-generator on Github. Simplest script and works like charm.