Google Image Previewing in Web Searches

It looks as if Google has added, yet another, feature to their web services array: when you do a web search which contains many image search results, Google will display a few thumbnails of top image search results above the normal search results. Though I could only get it to work with one word: qwerty. The other words I tried were for things that have many many pictures connected to them, like:

britney spears

dog

cat

I am starting to think that, maybe, Google is deciding what search-result pages to display pictures on by how many people jumb to the "Images" tab from the search-result page.