Heyo @dez1337
I will give you an example. Let's say you take an image from Imgur or other similar website (even Facebook).
What happens there is that the tool will say that the source of the Image is Imgur or Facebook. But the original source of the Image is actually the person who uploaded it. In which case the tool is wrong.
(Similarly if you upload your own image, though then you don't have to 'quote' the source)

But if you just get the image from Google search, blog post, website, then it'll work just fine.

Is that more clear?