Beginning soon, Google+ users will be able to take screenshots of content within a Hangout using the new Capture tool. Once the feature rolls out, simply click the camera button at the bottom of the Hangout window to grab a frame. The addition helps to simplify workflows a bit, while also serving to boost privacy -- unlike third-party screenshot offerings, this integrated tool notifies fellow users in your Hangout whenever someone enables the feature and when a picture is taken. Additionally, snaps are saved to a shared album, which other attendees may access from within the Hangout or through your photo albums. Privacy-obsessed users beware, though: You'll only be notified if the official Google tool is used -- apps like Skitch and Grab can still snag frames without a public warning.
Source:Jeremy Ng (Google+)