First, head to your Flickr account and click on the "You" button in the links listing. This will take you to your Flickr photostream.

Next, copy the URL in the address field of your web browser. This URL should appear to match this schema: "http://flickr.com/photos/YourUserNameHere". Once you have this URL, we can continue with screen saver creation.

Since the Flickr photostream doesn't automatically convert images into a Mac OS X RSS screen saver-supported format, we need to use an RSS feed converter called BIG Flickr Feed. It takes your existing photostream and rebroadcasts it with properly sized photos. Open http://www.bigflickrfeed.com/ in your web browser, and paste in the Flickr URL that you just copied. Then, click on the Go button.

The service will then give you a new RSS feed URL. Copy this URL. We will use it next to create the screen saver in OS X.

Next, head to System Preferences > Desktop & Screen Saver > Screen Saver. From here, click on the Plus (+) button below the screen savers listing. From the pop up menu, choose Add RSS Feed.

From the drop-down panel, enter the RSS feed URL that you received from the BIG Flickr Feed page and click OK. After validating the RSS feed, you will be able to continue setting your screen saver options.

After the RSS feed validation, your screen saver will show up in under the Pictures screen saver heading. You can switch between the different styles by using the Display Style selector. You can choose between: Slideshow, Collage, or Mosaic. All of your other picture screen saver options will also be present.