Flickr Tab is a Google Chrome extension which displays a different Flickr image every time you open a new tab.
That's essentially it. There are no complex settings here. There are no simple ones, either. You can't define the type of images you'd like, set up custom searches or do anything else. The extension just grabs a pic, displays it, and offers a small amount of interactivity (refreshing the page gets you a new image, clicking the photographer's name displays more from them).
This doesn't matter much, of course, because Flickr has some amazing images, and even if you don't like one, you'll be using your new tab to open a website about half a second later anyway.
It all worked very well for us, but may not be the right extension for everyone. If you like your new tab to open at Google, say, or display your bookmarks bar, then getting a Flickr image instead will only slow you down.