Ever been in the unfortunate situation where your game includes certain resources the author(s) of which you forgot to credit, so you don't know where they came from? Fortunately, it's usually easy to locate them with a reverse image search.
Here I have some pigs made by whtdragon.
(Her terms state, "I don't even mind if you re-upload them elsewhere", so I'm including them here legally.)
Now, let's imagine that I downloaded them a year or so ago and put them in my farming game. Sadly, I forgot to credit, and I don't know where they came from.
Go to google.com and head up to "Images."
Hit the camera button.
Paste in an image url or upload an image.
Scroll through your results until you find what you're looking for. You may need to scroll down a bit until you see "Pages that include matching images".
As you can see, I was able to find the original thread without a hitch.
Google may not turn up the results you're looking for. If not, you can try using TinEye. TinEye works quite differently from Google Image Search - which can be good or bad.
Using TinEye I was not able to find whtdragon's pigs. However, I have used it to find resources in the past that Google did not catch. So you could try using it and see if you get lucky.