How do I measure the amount of information within an image?
My problem with Shannon's entropy is that it is calculated without considering spatial structures.


That's not true!

Entropy is the expectation of Information, which is the negative logarithm of probability.

So, if you have correlated pixels (for example, in pictures of the first kind, say, a pixel in anything but the top row always has the same value as the pixel above), then that pixel's info drops to zero.

So, your statement is only true if you assume all pixels to be independent, which they aren't.