phpgeekfr

This plugin replaces author links of your posts with your Google+ Profile Link. 
This allow your Google+ Profile picture to be displayed in Google search results. 
It Works for single author and multi-author WordPress sites.

Basic Google Authorship

This plugin replaces author links of your posts with your Google+ Profile Link.

Mervin Praison

This plugin helps you add Google authorship markup to your WordPress site, allowing your Google Plus profile picture to appear in Google Search results.
Features: 
* Easy 4-step setup process 
* Multiple author support 
* Multisite compatible 
* Shortcode support

WP Google Authorship

Nice

Google Plus Profile Picture appear in Google Search. Very Easy to implement. Including Google authorship for multiple authors and multisite.

Basic Google Authorship vs WP Google Authorship