To me, it sounds like they did all the heavy lifting for the NSA, and then packaged it up as a "feature" for us. If Google handed over the emails themselves to the NSA, it would contain a lot more noise, but now it's really simple for the NSA.

The work is obviously to sift through all the emails, remove the photos, and separate/store them on a separate server. Now all NSA needs to do is get a daily dump of all the pics, and then run their data collection/facial recognition on them.