Google Search by Image API?

You can easily search by an existing image by inserting this into your address bar: https://www.google.com/searchbyimage?site=search&sa=X&image_url=YOUR_IMAGE_URL Example: https://www.google.com/searchbyimage?site=search&sa=X&image_url=http://cdn.sstatic.net/Sites/stackoverflow/company/img/logos/so/so-icon.png