Tom's brother posted it on his instagram account. I don't know if his account has always been private or if someone had the brilliant idea to link to it when reposting the picture which drove him to make it private. I hope it's not the latter because people should really know better by now unless they're new to the whole fandom thing.
I didn't keep the link to where I found the picture because I'm clearly useless, but I'm pretty sure it was a Thailand account. Possibly EmmaWatson_th. Sorry if I got that wrong.