Creative Commons Finder 2013 is a tool which helps you locate Flickr pictures published under the Creative Commons Licence, which can then be republished and reused however you like.
The program is simple enough to operate. Just type in your search term - "Christmas", "Beach", "Tiger", whatever you need - and various matching thumbnails appear. Clicking any of these displays it in a larger view, and you can then download the picture, set it as your wallpaper, or visit its Flickr page with a click.
While this works just fine, one significant problem is that the default settings will often find very few pictures. We entered "dolphins", for instance, and find only two images, neither of which you'd probably want to use.
There are ways to improve the situation. Choose to search for "pictures that may only be used with a reference to the author", for instance, and you'll see considerably more results. (Plus you need to think carefully about your search terms; entering a singular "dolphin" also returns more pictures than using "dolphins".)
If you need to search Flickr for images from your desktop then Creative Commons Finder 2013 might be helpful, at least sometimes. But on balance we'd still prefer something like Google Images. It can also search for pictures which can freely be reused, even commercially, but will usually give you many more photos to choose from.