Post score on facebook wall in unity3d

Question

I made a game in unity3d and share score on facebook wall. I used this

private const string FACEBOOK_APP_ID = "1624727317787654";

private const string FACEBOOK_URL = "http://www.facebook.com/dialog/feed";

and my code of sharing is

void OpenUserFBWall (string linkParameter, string nameParameter, string captionParameter, string descriptionParameter, string pictureParameter, string redirectParameter) {

    Application.OpenURL (FACEBOOK_URL + "?app_id=" + FACEBOOK_APP_ID +
                         "&link=" + WWW.EscapeURL(linkParameter) +
                         "&name=" + WWW.EscapeURL(nameParameter) +
                         "&caption=" + WWW.EscapeURL(captionParameter) + 
                         "&description=" + WWW.EscapeURL(descriptionParameter) + 
                         "&picture=" + WWW.EscapeURL(pictureParameter) + 
                         "&redirect_uri=" + WWW.EscapeURL(redirectParameter));
}

public void ShareToFacebook(){
    OpenUserFBWall("https://www.e-alyss.com/interactivity-details.php?iid=2&cid=62", 
                   fb_msg_type + score + "%",
                   "My Game",
                   "Wow! This is amazing", 
                   "http://server.vishal.com/games/icon/fb-share.png", 
                   "http://www.facebook.com/");
}

My problem is that, pictureParameter icon not shown when I post on facebook. My icon size is 319 x 350 Any help will be gracefull.

Thanks....