STEP 1: Save the photo to your desktop or somewhere on your hard drive.
STEP 2: Go to Google and click on "images."
STEP 3: Click on the camera icon in the search bar.
STEP 4: Click on the "upload an image" link.
STEP 5: Click on the "choose from" button.
STEP 6: Find the image that you saved on your hard drive.
STEP 7: Select "choose."
STEP 8: Google will automatically start searching the Internet for your image. The link you're looking for may not necessarily be the first one. Check 'em all until you find what you're looking for. Google will also pull up some similar images.
I had been looking for this incredible giraffe nursery online and this nifty little tool found the original source! Thanks Linde Browning Design for your to die for nursery and to Google for finding it for me! Woot!