They are not created by any human actually, let alone designers, or downloading from the Internet, or from some other people's photos.
They are rendered by iOS offline. Check the black and white stones, the light is cast at the upper left center part (about (0.25, 0.25 if viewing a stone in the unit square), and gradually spreads to the whole stone. Further zooming it in using Mac's preview and captured it as shown below (a little blurred as it is zoomed by preview without using super pixel technology).
I guess that the cost for generating the stones may (or may not) be more expensive than hiring a designer. As it takes the time to code and many iterations to reach a satisfactory stone. At least they look decent.
And it matches the shadow well (Please check other popular similar apps for shadow. And see if they can zoom in or not.)
Guess where the board texture is from? Again, it is generated, instead of copying from random background files from Internet, or from some uploaded photos.
Why do the author prefer this way? First it avoids copyright issues. And for computers, it is a pure environment with only physical laws to govern the output results, without affected by any ambient light. It has something the author pursuits, the purity.
If you like this work by computers, you may like it more after my explanation (or feel cheated). If you dislike, you can continue to say something "or, it is not from designers, not even human, poor crab work." (or change your mind). But the author accepts that it is natural. Whatever solution, it cannot satisfy all. Human beings are different:)
