pip install pyssim

$ pyssim --help
usage: pyssim [-h] image1.png image path with* or image2.png
Compares an image with a list of images using the SSIM metric.
  Example:
    pyssim test-images/test1-1.png "test-images/*"
positional arguments:
  image1.png
  image path with* or image2.png
optional arguments:
  -h, --help            show this help message and exit
  --cw                  compute the complex wavelet SSIM
  --width WIDTH         scales the image before computing SSIM
  --height HEIGHT       scales the image before computing SSIM

PYTHONPATH="." python ssim

pylint --rcfile=.pylintrc -r n ssim setup.py

$ PYTHONPATH="." python ssim test-images/test1-1.png "test-images/*"
test-images/test1-1.png - test-images/test1-1.png: 1
test-images/test1-1.png - test-images/test1-2.png: 0.9980119
test-images/test1-1.png - test-images/test2-1.png: 0.6726952
test-images/test1-1.png - test-images/test2-2.png: 0.6485879