Google started to make the iframes less important when it moved them to the background. Then the mobile interfaces for smartphones and tablets came out and they didn't even load the original web pages. The new desktop interface is closer to the tablet interface: click an image result and use the left/right keyboard arrows to check the other results.
Here's the old interface (you may still see it):
"Instead of sending you over to a whole new page to preview an image, you'll see a preview of the image in your search results. Once you click on a image, you can quickly flip through the whole set of image previews using your keyboard. Your search results stay in the panel so you don't lose track of what you were doing; if you want to go back to looking at other search results, you can just scroll down and pick up right where you left off. If you want to check out the website where the image is hosted, you can click on the photo or use the tools available," explains Google.
Obviously, the traffic from Google Image Search will drop dramatically and webmasters will complain that Google uses their images and doesn't give anything in return. Google only hosts image thumbnails and loads the original images when you click the thumbnails, so it's now an image leecher that hotlinks to other people's images, using their bandwidth without generating page views or ad revenue. It's better for users, but expect to see many sites that stop displaying images when loaded from Google Image Search or use other anti-leech tricks.
Finding the right balance between user experience and webmasters' interests is a hard thing to do. Google now includes 4 links to the original web page, so you can click the image, the page title, the domain name and the "visit page" button, but I bet most people will click "view original image". Unfortunately, Google no longer displays two very important things: the image title and a short snippet from the page related to the image. Showing only the title of the page and the domain name is not enough to determine if the image is relevant. Other missing information: the EXIF data and the image size.