Here is the project file used in my tutorial, Optical Flow in Houdini 16.5. It includes the image sequence used to drive my original Paint Party animation and is similar to my original setup file, but reworked to run with the new Volume Optical Flow node in Houdini 16.5 (Indie and Apprentice only). Project file is provided as-is and is intended for educational purposes. Learn, Play, Make, Enjoy!
Update 1/1/2019 - If you're following along using Houdini 17 and getting stuck around the sourcing part, I've added a modified setup here that takes a particle field and sources into the Dopnet using the new Houdini 17.0 Volume Source node. I hope this helps!