getting first image of article for open graph

Question

I've been a PHP developer for long time, but I am new to Joomla. On a Joomla 2.5 project, I need to make open graph meta tags. As a part of open graph meta tags, I need to find first image of article. I tried many, many ways suggested in forums and articles, but none of them worked.

This is a sample of what I tested in template file:

$article = & JTable::getInstance("content");
$article->load(JRequest::getInt("id")); 
$url = JURI::current();
$title = $article->get("title"); 
if (strpos(".html", $url) != 0) {
    $type = "website";
} else {
    $type = "aricle";
} //opengraph

$article_images = $article->get("images");  
$pictures => json_decode($article_images);

$timage= $pictures->{'image_intro'};
?>
<meta property="og:title" content="<?php echo $title ?>" />
<meta property="og:type" content="<?php echo $type ?>" />   
<meta property="og:url" content="<?php echo $url ?>" />     
<meta property="og:site_name" content="beytoote" />     
<meta property="og:image" content="<?php echo $timage ?>" />

but it did not worked.

And this is a sample of what I tested inside a block:

<?php //opengraph $doc = JFactory::getDocument();
if (preg_match('/<\s*img[^>]+>/Ui', $this->item->text, $matches)) {
    $image=$matches[1] 
} 
$doc->addCustomTag( '<meta property="og:image" content="' . $image . '">' );
?>