Find an image with an image
There's an incredible application developed by a Canadian company, Idee Inc., which can scour the web for an image using... the image. Wha? Say you are a photographer who sells your images for use but also post samples online, you can find out who has been using the pics online with and without your permission. Or as a company that needs to rebrand or manage brand, you can search your own logo and corporate brand images online to see if they are being used properly; or to request that they be changed to the new brand, if appropriate. It's all very kewl.
One really neat example of this at work is on the Idee Inc. blog. There is stock photography of a female model from the early '90s which is used a lot (she's even on a magnet I have on my fridge for the Canada site). Idee Inc. loaded her pic into their app and set off to the web to see where they could find her. Well, they found her everywhere. Which makes sense, since her nickname is "Everywhere Girl". Read the Idee Inc blog article