<?php
$hash = 'x,x/b2m5kaaj=i46+M#';
// Good URL from chess-4
// http://images.chesscomfiles-4.com/uploads/user/41.02d5743c.200x200o.3e7c6cd0544f.png
var_dump(md5("user/41.02d5743c.200x200o.png".$hash));
// Your example
// user/1906698.8482bae0.200x200o.46e9c046f2d9.jpeg
var_dump(md5("1906698.8482bae0.200x200o.jpeg".$hash));