Articles linked on Facebook don't display thumbnails images

Hi,

I need help with the following:

Problem: Articles linked on Facebook don’t display thumbnails images. Facebook like/share doesn’t represent my posts properly. It chooses the first picture which happens to be my post title.

2. I’m using two plugins:

a. Tweet, Like, Share and Google +1 Option Page
b. Simple Social – Sharing Widgets & Icons

How should I modify the facebook plugin so it will show my second image all of the time (my first is the title)when someone press like/share button?

At ‘Tweet, Like, Share and Google +1’ plugin code, there are two attributes which define the og:image:

<meta property="og:image" content="<?php echo $thumb; ?>" />
<meta property="og:image" content="<?php echo $default_img; ?>" />

function s4_get_first_image() {
global $post, $posts;
$first_img = '';
ob_start();
ob_end_clean();
$output = preg_match_all('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches);
$first_img = $matches[1][0];
return $first_img;
}

From the code, the point where I need to define the picture number is:

$matches[1][0]

Should I change it to $matches[2][0]?

Thanks and regards,

Kfir Silis