Found a bunch of sites with this gif (or lower-quality versions of it), but unable to find the full-length clip.
Most seem to have "analfeet.tumblr" watermark on the lower-right, with a cut off "...ry.com" watermark on the lower left.
TinEye first saw it in late 2014: https://tineye.com/search/279f95adbfe28fffb12c62855d57bbb03c9235ff/
Very interested in finding the full clip!
Looks like analfeet.tumblr.com was mostly active in 2012-2013 (according to wayback machine). When the machine tried in 2015, the site was already gone.
The watermark on the lower left does seem to be the contemporaneous 21sextury.com logo; found lots of other images on the wayback version of that tumblr with the same font / trapping.
Anal Training of Karen & Ioana
Thanks!
I'd gotten as far as http://www.21sextury.com/en/video/Anal-training-of-Karen--Ioana-Scene-01/97298 but hadn't hit "play" yet.
Thanks, mate!