Hey Sophie! I felt pretty strongly that I did not want to resort to pirating any movies, so my process for getting the movie color data is pretty manual. First I rent or buy the DVD, then I convert it into a digital file, then I use Processing’s Video library to read it frame-by-frame. The whole process takes a while.
For the comic book project, I purchased the comic books digitally. Back then, Image Comics provided their digital comics in a DRM-free PDF, which I then converted into image files. (Since then, Image Comics has added DRM so this process will no longer work.)
So to answer your question, I would recommend you either rent the DVD to convert it to a digital file, or find a way to purchase the books in a digital format that you can then read.
One of the fun things about those projects is that they usually take many steps. I don’t go straight from DVD to an image showing the colors in the movie. I first figure out how to convert a DVD to a digital file, then I figure out how to read in a digital movie file, then I figure out how to convert that movie file into a series of frames, then I figure out how to get the average color of a single frame, etc.
This process of splitting a problem up into multiple steps and then taking each step one at a time is the key to these kinds of large projects.
Good luck! I’ll be very curious to see what you come up with!