if I draw something on a piece of paper, scan it, and hash it, there's no way anyone (including me) can ever reproduce it!
It'll definitely be messed up, but not random, or at least not as much as in other ways. There's a significant percentage of the human factor, how does your hand move, which shapes will you think of, at which rate will you repeat the shame shapes etc.
It's not only about the drawing, it's about the scanning. Or take a picture: you'll get millions of pixels, and each of them will be slightly different. Even if you draw the same thing, or even if you scan the same piece of paper again, it will be different. Hashing it means a totally different result.
I would say it's infeasible today (and maybe even forever) to crack, however the entropy is definitely lower than true randomness, since images are generally not truly random pixel distributions. The scanning software and hardware could also add artifacts that are very repeatable patterns (even though invisible to the human eye), which weakens the randomness further.
It's common knowledge that 'humans can't really understand large numbers'.
For example, we know that a million, a billion and a trillion are massive numbers — but most people have a hard time understanding how significant the difference is between them.
There are theories about our brains working on a log scale instead of linear and ideas like this, but I don't know if anything's really proven today.
I digress; you're right when you say
there's no way anyone (including me) can ever reproduce it, but that doesn't mean it's nearly 'as random' as coin tosses.