open graph image script in meta

My facebook is grabbing the wrong image.

I try to adding this open graph image in my head.

<meta property="og:image" content="<?= $_GET['image'] ?>" />

and

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

but the content image path is not shown. It became this

<meta property="og:image" content="" />

I want it to be like this. If the article A have image a_name.jpg, the meta will be <meta property="og:image" content="/images/a_name.jpg"/>

If the article B have image b_name.jpg, the meta will be <meta property="og:image" content="/images/b_name.jpg"/>