If you've ever played a game of "Telephone," it's easy to understand why Pinterest's guideline number three, "credit your sources," is the most important Pinterest rule there is. In "Telephone," a player whispers something in another one's ear. The information passes around the circle until it winds up whispered back into the ear of the original speaker. Invariably, the original message becomes garbled. So it can be with pinning.
Say you create a pinboard called "famous pictures I love". Remembering that old, World War II-era, black-and-white photo of a sailor roundly kissing a nurse in the middle of Times Square, you Google "famous photo navy kiss" The search turns up multiple copies of the image. As in "Telephone," the first instance you find may have been copied from a copy that was itself copied. With a bit of digging, however, you'll be able to identify Alfred Eisenstaedt as the photographer and you'll find a legitimate source, LIFE Magazine, which famously published the photo in 1945 [source: Life Magazine]. If you don't take the time to dig up an original (or at least a legitimate) source, you risk copyright infringement and you rob your followers of the chance to learn more about Eisenstaedt.
And about your followers, learn how to find and interact with them next.