Here's a bit of an esoteric issue that was a bit tricky to hunt down. I hope that this blog post helps the few people out there that it applies to!

You've got a secure (https) Drupal site, and you'd like it to contain facebook-compatible, open graph meta tags. So, you download the meta tags module and do some configuration magic. Everything looks good until you post a page on Facebook, and the image doesn't work!

Apparently, Facebook doesn't play nice with og:image tags served over https.

Ok, so let's not serve our og:image tags over https. A quick theming hook will fix that in no time:

/**
* Theme callback for an OpenGraph meta tag.
*/
function THEMENAME_metatag_opengraph($variables) {
$element = &$variables['element'];
switch ($element['#name']) {
case 'og:image':
$element['#value'] = str_replace('https://', 'http://', $element['#value']);
break;
}
 
element_set_attributes($element, array('#name' => 'property', '#value' => 'content'));
unset($element['#value']);
return theme('html_tag', $variables);
}

For most people, you can just clear your cache and you'll be set. However, I forgot about my htaccess rule that directed all http requests to https. If you have a similar rule, you'll need to make an exemption for file requests (or perhaps just file requests to a certain directory). For me, that looked something like:

RewriteCond %{HTTP:X-Forwarded-Proto} !=https
RewriteCond %{HTTP_HOST} ^www\.obfuscate\.com$ [NC]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)$ https://www.obfuscate.com/$1 [L,R=301]

An then it worked! Yay.

If you're still having trouble, checkout these useful tools:Web sniffer -- See what the bots are seeing.Facebook debugger -- get some insight from the FB developers!

7.x,
drupal, facebook, og:image, meta tags, https, htaccess