Search Images using an Image

Normally, searching photos on the web involves typing some keywords. TinEye is a different type of image search engine though. Here, its not keywords; images are used.

Just go to TinEye and submit an image to it.

TinEye finds exact matches of images including those that are edited, resized or cropped.
This can be used to -

a. find out if someone else is using your images,
b. find modified versions of your pictures,
c. find a higher resolution of the same image.

Check out some example searches provided by them here.