How to use drupal_add_html_head() to add the same metatag multiple times?
The tags are stored by key, so using a different key for each should do the trick:

$delta = 0;
foreach ($images as $image) {
    $element = array(
        '#tag' =&gt; 'meta',
        '#attributes' =&gt; array(
            "property" =&gt; "og:image",
            "content" =&gt; $image,
        ),
    );
    drupal_add_html_head($element,'facebook_share_image:' . $delta++);
}