I'd say they're not GIFs, they're embedded mini-websites with their own tracking cookies and JS and whatnot. If only they were GIFs.
If you load it in a browser you get an entire HTML page full of spyware - it is not a GIF. They're detecting the user agent and deciding whether to send spyware or not - only curl'ing the link gives you the raw GIF by the looks of it.
I'd say they're not GIFs, they're embedded mini-websites with their own tracking cookies and JS and whatnot. If only they were GIFs.