Google has released an interactive similar images explorer. The app is called Google Image Swirl, and it’s using the wonder wheel Flash visualization you might know from web search results.
Here’s how it works: you enter a query, like “lion”. After a bit of loading, and if your keyword is supported (not all queries are), you’ll be presented with some visual base categories Google could find:
Opening a category by clicking on it will start the star exploration, with your image in centre, surrounded by similar images. Clicking on a surrounding image will put it in focus, and new surrounding images are loaded dynamically:
Once you reached a final image with no more new neighbours, a click on it will take you to the original source site it’s crawled from:
In all of this, even due to its scripted Flash nature, the back button will take you to your last focus image. The app is fast, accessible, scaling pretty well to many keywords (not all – Google mentions there’s 200,000 at the moment), and on first glance it looks useful, too.