I created following meta tags in head
<meta name="image" content="image url" />
<meta name="title" content="Page title" />
Now I used following code to extract URL and then the tags
$url='http://' .$_SERVER[ 'HTTP_HOST'].$_SERVER[ 'REQUEST_URI'];
$tags = get_meta_tags($url);
$image = $tags['image'];
$title = $tags['title'];
The page however keeps loading and outputs nothing.
It's look like you call get_meta_tags script itself? If yes, you get infinite recursion and output nothing. Page keep loadings, and in the end, of course, would be a mistake - exceeded the maximum execution time.
How do you expect to see something if you're just assigning a variable and nothing else?
Do var_dump($image) and then for example die() to see it's content... or whatever you need.