brahmnan

If you want user avatars to be displayed quickly and do not use external services, the module for generating “identicon” avatars using “canvas” is suitable for you. 
“Canvas” avatars will be generated for all users who do not have their own avatar images.

Identic canvas

This plugin creates user "identicon" avatars in "canvas" format using user email

Nazmul Hossain Nihal

This allows user to add a widget that generates QrCode for every page dynamically. Whenever a visitor visits the site the widget will show qrcode for current page that the visitor is visiting. User can add the widget with and without title, define the size of the qrcode, fill color and background color. If the user finds that widget is not working because of any problem with theme user can add custom HTML tag before and after the widget. Multiple widgets can be added same time.
Using this you can add favicons to :
<ul>
<li>Add QrCodes</li>
<li>Customize QrCodes</li>
</ul>

WpQrCode

Just another WordPress plugin for adding QrCode.

Identic canvas vs WpQrCode