orbisius-fb-open-graph-tags.php

<?php
/*
  Plugin Name: Orbisius Facebook Share Image Preview Fix
  Plugin URI: http://orbisius.com
  Description: Makes sure that post's featured image is 1200x630 so facebook can use it as preview.
  Version: 1.0.0
  Author: Svetoslav Marinov (Slavi)
  Author URI: http://club.orbisius.com/products/
 */
 
add_action( 'wp', 'orbisius_og_tags_init', 100 );

/**
*/
function orbisius_og_tags_init() {
	add_action( 'wp_head', 'orbisius_og_output_tags' );
}

/**
 * Outputs a header instruction
 * @see http://davidwalsh.name/demo/facebook-metas.php
 * @see http://stackoverflow.com/questions/11616697/how-to-use-og-meta-tag-for-facebook-share
*/
function orbisius_og_output_tags() {	
	global $post;
	$id = get_the_ID();
	
	/*if ( ! defined( 'orbisius_APP_POST_TYPE' ) 
			|| 'post' != get_post_type( $id ) ) {	
		return;
	}*/
	
	/*
	[0] => url
	[1] => width
	[2] => height
	[3] => boolean: true if $url is a resized image, false if it is the original 
		or if no image is available.
	*/
	// Make facebook happy.
	// @see http://webgilde.com/en/wrong-image-facebook/
	$img_src_rec = wp_get_attachment_image_src(
		get_post_thumbnail_id( $id, array( 1200, 630 ) )
	);
	
	if ( empty( $img_src_rec ) ) {
		return ;
	}
	
	$img_src = $img_src_rec[0];	
	
	/*
	<!-- for Facebook -->          
	<meta property="og:title" content="" />
	<meta property="og:type" content="article" />
	<meta property="og:image" content="<?php echo $img_src; ?>" />
	<meta property="og:url" content="" />
	<meta property="og:description" content="" />
	
	<!-- for Twitter -->          
	<meta name="twitter:card" content="summary" />
	<meta name="twitter:title" content="" />
	<meta name="twitter:description" content="" />
	<meta name="twitter:image" content="<?php echo $img_src; ?>" />
	*/
	?>
    <!-- Make Facebook happy: 1200x630-->
	<meta property="og:image" content="<?php echo $img_src; ?>" />
	<!-- /Make Facebook happy: 1200x630-->
	<?php
}