If you search for something using Google Images that is trending, timely or specifically newsworthy, your results will now show recent images first. Results will be shown with timestamps on the bottom right corners.
Google has been showing recent results in normal search for a while, but the recent results were just spotted for images this morning. If I search for 'Rory McIlroy" (the young Irish golfer), I am not given image results listed by recency. But if I search "McIlroy Masters," I am given images from yesterday's golf tournament at the top of my page.
This is not the only change to Google images search as of late. At the beginning of the month, they made improvements to the "similar images" feature.
Thanks to Barry Schwartz at Search Engine Land.