How to Prevent Google From Using Your Face in Ads
The new program is called 'Shared Endorsements'. Google touts it as an easy way for you to get great recommendations from your friends. However, it does warn that "To help your friends and others find cool stuff online, your activity (such as reviews, +1's, follows, shares, etc.) may be used along with your name and photo in commercial or other promotional contexts."
To opt out of this program click the link below and navigate to the bottom of the page. Uncheck the box that reads: Based on my activity, Google may show my name and profile photo in shared endorsements that appear in ads. Then click the Save button.