The acquisition, which has been in the works for more than a year, is expected to close this week, the person said.
Representatives from Google and Viewdle declined to comment.
The move makes sense for Google because Viewdle's technology provides a way for users of Google+, Android, Picasa, and other services on a range of devices to easily (even, automatically) tag photos of friends. Viewdle's SocialCamera app automatically tags Facebook friends and the company has released an Android game called Third Eye.
Facebook also has made a play in this space, earlier this year buying Face.com along with its Photo Tagger auto-tagging app.
The Google-Viewdle deal, which could close as soon as tomorrow, was started with talks between Motorola and Viewdle before the handset maker was acquired by Google last year, according to the source, who asked not to be named. The purchase price is toward the high end of a $30 million to $45 million range, according to the source.