Earliest source I'm capable of finding is on Gelbooru, but that doesn't possess the barefoot variant. So either the barefoot is a really REALLY well done third-party edit, or the uploader on SakankuComplex had found a source that contained two versions.
Also both uploaders have been inactive for over three years.
[EDIT] I am SO DUMB. It was sourced over on footfetishbooru.