A simple software for calculate mutual information and users can resize the image simultaneously
Mutual Information gets lower when the difference between images is bigger. If two images are the same, the MI shall be over 1 bit.
In the figure below, we can see that the sunset glow structure between two paintings is similar so the mutual information attain 0.7.
If you are interested, a demo is in https://pan.baidu.com/s/1QZ77K88c89KLZdTHysaxxg mikl