First time here? Check out the FAQ!
Upgrading webp with homebrew solved issue in my case:
brew upgrade webp
p.s.
before upgrade I had 0.4.4 with libwebp.5.dylib in /usr/local/Cellar/webp/0.4.4/lib
0.4.4
libwebp.5.dylib
/usr/local/Cellar/webp/0.4.4/lib
after upgrade it is now 0.5.1 with libwebp.6.dylib in /usr/local/Cellar/webp/0.5.1/lib
0.5.1
libwebp.6.dylib
/usr/local/Cellar/webp/0.5.1/lib
>>> import cv2 >>> cv2.__version__ '3.1.0'