Vincent Mo, Google+ Photos engineering lead, announced the new feature on his Google+ profile Thursday, saying that it was one of the top requests for Google+ Photos.
In order to +1 a photo, click on it to open the photo viewer. You’ll see the +1 button at the bottom left side of the photo.
The feature is now available on the Google+ iPhone app and will soon be added to the Android app and mobile site.
With its expanded functionality, the +1 button looks even more like Facebook’s “Like” button — a simple thumbs-up that works across any type of content. As Facebook makes its buttons more specific with “Facebook Gestures” that allow people to watch, listen and read (but not “dislike”), it will be interesting to see if +1 follows suit or breaks the mold. Perhaps the -1 button?