We have already posted about this feature which was one of the many limited experiments conducted with a set of users by the company.
Google has now officially launched the improved related image searches functionality on Google Image Search engine.
The related searches are shown at the top of image results and you can hover on them to get a preview of the results.
Google spoke about this feature improvement:
Today we’re making it easier for you to hone in on that perfect image or explore your topic visually with an update to related search links. Related search links have been around for a while—they’re the row of blue links running across the top of your image search results—but today we’re making them more visual to help you find exactly what you’re looking for or just have fun exploring.
They are rolling out this update to all users. It could take a couple of days before you can see it on your own account.