I just started using the really cool WordPress plugin called PhotoDropper.
It essentially let’s you harness the power of WordPress, Flickr and the Creative Commons Licensing scheme to use images others have shot and are willing to share (yes, to use on your blog). All you have to do is to adhere to the correct Creative Commons License that is attached to the photo.
You can do the image search from within the Write screen in the WordPress admin area. It will format the pic with links that are needed to comply with the license automatically, plus you get to choose from 3 sizes of the image to insert.
This makes it very easy to find an appropriate image for the theme of your post if you don’t already have one in your image library.
The site Skelliewag.org has a great explanation of what these 6 different Creative Commons Licenses are for. I’ll just let them it explain that part for you.
Another explanation of using photos from Flickr can be found on Internet Marketing with Josh Spaulding. He goes into a good deal of detail about this topic.