Create a facebook share button adding a cusatom thumb-image

Hi

I've done this code for create a "suggest site" button for facebook

PHP Code:

---

facebookbtn.addEventListener(MouseEvent.CLICK, function()
{
      openPage('http://www.facebook.com/sharer/sharer.php?t=mysite&u='+escape("http://www.mysite.com"),"_popup");
})

function openPage(url:String, linkWindow:String = "_blank", popUpDimensions:Array = null):void 
{
            if (linkWindow == "_popup" && ExternalInterface.available) 
            {
                var dimensions:Array = [800,600];
                ExternalInterface.call("window.open('" + url + "','PopUpWindow','width=" + dimensions[0] + ",height=" + dimensions[1] + ",toolbar=yes,scrollbars=yes')");
            } 
            else 
            {
                // Use JS to bypass popup blockers if ExternalInterface is available
                var window:String = linkWindow == "_popup" ? "_blank" : linkWindow;
                if (ExternalInterface.available)
                {
                    ExternalInterface.call('window.open("' + url + '","' + window + '")');
                } 
                else
                {
                    //request a blank page
                    navigateToURL(new URLRequest(url), window);
                }
            }
        } 


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It wotks, but if i want to add an image thumb how i can do? Searching on google i've found this answer

Quote:

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For use a picture you need to share the page has some Metatags.
<meta name="title" content="my title" />
<meta name="description" content="my description" />
<link rel="image_src" href="images/thumbnail_image.jpg" />

---

how i can add it calling the external interface?

Thanks