Go to https://images.google.com and click the camera icon.
And either upload or paste the direct link to the image. It will search for any website that has the same and will sometimes help you find the source.
How do you find the original source for a photograph uploaded to the net?
There's a browser add-on called TinEye which allows you to do a reverse image search. It will find any other instances of the same image on the Web and, from that, you may be able to decide which is the original
