I used clipart a LOT for newsetters and other documents. I don't always want a photo - clipart is often better at getting an idea across quickly, and I didn't need to worry about copyright because I assumed it was OK to use without permission as it was a part of the MS package. The BING option is terrible - very juvenile and hardly extensive with fewer than 50 options. And by-the-way, most of the online sites for "accessing clipart in MS Word 2010" still say to go to insert then click on clipart. Really - we hardly need such basic instructions when they aren't even correct anymore!
Bing Image Search uses a copyright filter based on the Creative Commons licensing system. The results that are returned are images that have been tagged with Creative Commons licenses. A link to the source of the image is provided, which you should use to review the source of the image and the applicable license to determine whether your use will comply with the license. (The settings can be switched to show all web results to view more images.) However, you are responsible for respecting others’ rights, including copyright. Learn more here.