I am currently writing a document that needs pictures for visual representations of my topic. I've been browsing around on the internet to find such picture. I found a very good picture on the internet that could be suitable for my topic. Unfortunately, I do not know how to cite this picture.
The reason why I say I do not know how to cite this picture is because it is a picture from a textbook (or article) that someone decided to upload on Pinterest. I know it's a picture from a textbook (or article) because the picture has a small caption at the bottom that says, Figure 1.2: Blah blah blah, on the bottom.
Is it possible to cite something like this? Should I move on and try to find a substitute?