Recently, Flickr gave all of its users 1 terabyte of free space. Reddit user rlaw68 shows how to utilise that space for more than just photos and videos.
The process involves combining the file you want to upload with a gif. Flickr checks the headers of the file, sees a picture and grabs the whole thing. Unbeknownst to the server, though, your file is tagging along in a makeshift zip package. As per rlaw68's instructions:
When you want to access it again, you just download the file, rename it with a .zip extension and open it like normal. If you're using a Mac, WonderHowTo also has a primer on how to accomplish this task.
This may not be useful for most situations. Flickr has an upload limit on photos of 200MB, and this process means that it's somewhat cumbersome for daily use compared to a service like Dropbox, but in a pinch, it never hurts to have a backup plan. In similar fashion, you can also hide files in a JPEG to keep data out of sight (though this won't solve the Flickr upload challenge).