[iandanforth]

FWIW I did some things in this area a while back and ended up needing to stream canvas state back to my Python scripts for image processing.

https://gist.github.com/iandanforth/0ed987bfddf8205b8a23

I hope that could be a part of this framework in the future! (If it isn't already)

[adrien-treuille]

This is really cool. We've been thinking about these issues to create an image masking widget in Streamlit. Would be interesting to connect when we start down that path. If you're interested, please feel free to connect over discuss.streamlit.io. :-)