Dennis

The QR Code Tag plugin creates QRCodes for your blog.
Features:
<ul>
<li>Choose your QR Code generator: Google Chart API (online connection required) or QR Code Lib (included)</li>
<li>Uses cURL if <code>allow_url_fopen</code> is disabled (Google Chart API) </li>
<li>GIF, PNG or JPEG image output</li>
<li>All QR Code images are cached</li>
<li>Use as a Sidebar Widget</li>
<li>Use the Shortcode <code>[qrcodetag]content[/qrcodetag]</code> within your posts</li>
<li>Use the Tooltip mode <code>[qrcodetag tooltip="content"]some text[/qrcodetag]</code> within your posts</li>
<li>Use the PHP function inside your own template</li>
<li>“Best Read Mode” for optimized QR Code image size</li>
<li>Works with PHP 5.3 as well</li>
<li>Works on symlinked plugin folders</li>
<li>Available plugin admin interface languages: English, German</li>
</ul>
<h3>Demo</h3>
See <a href="http://www.spreendigital.de/blog/2009/09/18/essential-android-applications/" rel="nofollow ugc">this blog entry</a> for a tooltip mode demo. 
Move your mouse over the application links.
<h3>Acknowledgements</h3>
This WordPress QR Code Tag Plugin is partly based on <a href="https://wordpress.org/extend/plugins/super-cool-qrcode/" rel="ugc">Super Cool QRCode Widget</a> by <a href="http://www.incerteza.org/blog/" rel="nofollow ugc">Matias S.</a>.
It uses:
<ul>
<li><a href="http://code.google.com/intl/de/apis/chart/" rel="nofollow ugc">Google Chart API</a> for online code creation</li>
<li>Y. Swetakes <a href="http://www.swetake.com/qr/index-e.html" rel="nofollow ugc">QR Code Library</a> for code offline creation</li>
<li>J. Zaefferers <a href="http://docs.jquery.com/Plugins/Tooltip" rel="nofollow ugc">jQuery Tooltip Plugin</a></li>
</ul>

QR Code Tag

Uncaught TypeError: $(...).tooltip is not a function

creates lots of errors with new wp

Use QR Codes (Google API or QR Code Lib) anywhere in your blog, as a Widget, Shortcode, Tooltip or with a PHP function.

Steven Vachon

If you were to use this on a website like http;//example.com/test/testing/, you would get results like these:
<ol>
<li>
<ul>
<li>Before: http;//example.com/test/another-test/#anchor</li>
<li>After: ../another-test/#anchor</li>
</ul>
</li>
<li>
<ul>
<li>Before: http;//example.com/wp-content/themes/twentyten/style.css</li>
<li>After: /wp-content/themes/twentyten/style.css</li>
</ul>
</li>
<li>
<ul>
<li>Before: https;//example.com/wp-content/themes/twentyten/style.css</li>
<li>After: https;//example.com/wp-content/themes/twentyten/style.css</li>
</ul>
</li>
<li>
<ul>
<li>Before: http;//google.com/test/</li>
<li>After: //google.com/test/</li>
</ul>
</li>
<li>
<ul>
<li>Before: ../../../../../../../../#anchor</li>
<li>After: /#anchor</li>
<li>After (<code>$output_type=1</code>): ../../#anchor</li>
</ul>
</li>
</ol>
All string parsing. No directory browsing.
If you’re looking for a plugin that will automatically convert all URLs on your WordPress site, instead check out my other plugin, <a href="https://wordpress.org/extend/plugins/wp-html-compression/" rel="ugc">WP-HTML-Compression</a>. 
Before you copy this code and add it into your own, keep in mind that there will probably be future updates. Keeping the code within an installed plugin will make sure that you’re notified.

Absolute-to-Relative URLs

A function() for use in shortening URL links. This plugin is meant for dev work and does not automatically shorten URLs.

QR Code Tag vs Absolute-to-Relative URLs