If you want to download all of those images so you can have a nice high quality screen saver on your laptop/mobile etc. just do this:
git clone -b patch-1 https://github.com/mattburns/chromecast-backgrounds.git
npm install lodash q request nopt chalk
node cli.js --download=images --size=1024 --load=backgrounds.json
Change the size from 1024 to whatever maximum size you want to download.
I had to tweak the source from this project on github. Hopefully my fork will get folded in.