TinEye is a reverse image search engine. What that means is that instead of searching for images by keyword like you would on Yahoo Images you search for images by uploading an image or linking to an image. For example, if I have a picture of my dog and want to find more pictures of dogs like him, I simply upload a picture of my dog to TinEye and TinEye will search for images like mine.
TinEye offers browser extensions for Chrome, Firefox, Safari, Internet Explorer, and Opera. With the extension installed you can simply right click on any image and select "search image on TinEye" to quickly conduct an image search.
Applications for Education
TinEye's browser extensions could be very helpful for students to quickly locate images to use in presentations. As I wrote a couple of years ago, TinEye itself could be useful for teaching students to be aware of their digital footprints. You could use TinEye to show them that an image they upload to a social network could get reused in multiple places.