Fetching files from disk at runtime

Hi. I'm trying to add a "modding" feature to my strategy game by allowing players to use a jpg file as a map. To do this i put a sprite object in the center of the scene, and made a script that reads from a file in the user's desktop to the game. I am using Loadimage and a WWW with a relative filepath to get the file called "myMap.jpg", but keep getting a NullReference exception. After almost two days of research, I can't figure out why. Please enlighten me.

Here is the code:

   void Start () {
             map = gameObject.GetComponent <Sprite> ();
         }
 
     void Update () {
         if (canLoad) {
             if (Input.GetKeyUp (KeyCode.P)) {
 
 
                 StartCoroutine (GitMap ("file://" + Application.dataPath.Remove (20) + "/myMap.jpg"));
 
                 Debug.Log (www.url);
                 //This debug confirms that the filepath is the one I'm looking for
 
                 if (www != null) {
                     Debug.Log (www.bytes);
                 }
 
                 tex.LoadImage (www.bytes); //here is the problem.
 
                 map = Sprite.Create (tex, new Rect (0, 0, tex.width, tex.height), new Vector2 (0.5f, 0.5f));
             } 
         }
 
 IEnumerator GitMap (string PATH) {
         www = new WWW (PATH);
         yield return www;
     }