How do you get bandwidth saving static GIFs?

[thescorpiotheory]

When tumblr app's data saving mode is turned on, it loads static (jpeg or a png?) versions of the animated gifs as previews and waits for you to tap to load the full sized resource heavy gifs. Ive looked through the photos array (and pretty much everything else) but i couldn't find any reference to these lite static versions. can some one please tell me how get to these bandwidth saving static versions of animated GIFs? 

Thanks.