I made a few fun plugins that would encode data (after deduping, compressing and encrypting them) into PNG or BMP and store them on Flickr (which gave you 1TB of free storage for images) or Picasa (now Google Photos). It was actually relatively efficient and not slower than the other methods, and it looked super cool to have albums full of what looked like images of static. It was a blatant violation of their ToC, so obviously not serious.
The code is still online, it's from 2014/2015. The Flickr plugin with the PNG encoder is here [3], and I'm not entirely sure if I ever published the Picasa one.
[2] https://github.com/syncany?q=plugin
[3] https://github.com/syncany/syncany-plugin-flickr/tree/develo...