Find images with info available on how to reuse them:
Search for an image.
Under the search box, click Tools.
To narrow results to images with available license info, click Usage rights and then choose a type of license.
Click the image you want.
To find info on how to license and use the image, below the image in the right panel, click License details.
Source: Google Search Help
Search by Image
Google Images also offers the option to search by image. If you already have an image and want to know where it comes from, who it is, etc. you can search Google Images for that particular image.
In the search box on the Google Images homepage:
Click on the camera icon in the search box.
Two options: Paste image URL / Upload an image