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:
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: