Google is facing a backlash over plans to put people's faces and comments about products and places into adverts.
The "shared endorsements" policy change starts on 11 November and covers the comments, "follows" and other actions people do on Google+.
One protest involves people swapping their profile pictures for that of Google boss Eric Schmidt so his image rather than their own appears on ads.
Google said it had made it easy for people to opt out of the system.
The search giant started alerting people about the upcoming policy change via banners on its main webpage and in a page explaining the change to its "policies and principles".
Google also gave examples of how the "shared endorsement" system might work. This showed people's faces and comments appearing below Street View images of a bagel shop and search results for products and places.
Many people protested about the change to Google, and some altered their image profiles on the Google+ social network in response.
So far, Google has not issued an official comment about the protests over "shared endorsements". However, in its explanatory pages it said it was easy to opt out of the system by clicking a box on the Google+ account settings page.
It warned that if people did not want to be part of the programme some of their comments and follows may no longer be visible to others they know on Google+.
Social network Facebook faced strong criticism over a similar system called "sponsored stories" it rolled out in 2011.
Legal action following the criticism eventually led to Facebook paying out $20m to compensate people whose images it used without permission.