After a month or so of testing, Google appears to have launched a new design and interface for the image search preview box. The new box shows the image in a larger frame, with more details about that image and related images. It also sticks to the right side, so you can scroll through the details without scrolling to see more images.
What it looks like. Here is a screen shot of this new interface:
Here is a GIF of it in action:
Old design. Here is a screen shot of the old design and interface:
Testing. Google has been testing variations of a new preview box in the image search results for months. Here are some links to previous tests and designs.
Why we should care. Any change to the way Google shows image results can lead to changes in traffic to your web site. So keep an eye out for any changes to your search traffic from Google Image search.
Postscript: Google has now confirmed this new feature and posted about it on its blog.