It can't.
Sorry. If you want lossy compression over a time index, then you have to find
other formats.
(Edited 20 seconds later.)
the image is a gif or an apng with the extension renamed to .jpg
the image keeps the .jpg extension, but still plays the gif when uploaded to a filehost
alternatively, the url ending in jpg links to the url ending in png or gif
(Edited 3 minutes later.)
it's crap like nokia's cinemagraph that saves animated gif in jpg to fuck us up inside
enjoy