Custom OG image WP

functions.php

define( 'FB_COVER_SIZE_NAME', 'fb-cover' );
function custom_theme_setup() {
	add_image_size( FB_COVER_SIZE_NAME, 660, 347, true );
  // more img sizes
}
add_action( 'init', 'custom_theme_setup' );

function lb_image_downsize( $value = false, $post_id, $size = 'medium' )
{
	$arr_size = get_image_size($size);
	if($arr_size && $img_url = lb_image_url($size, $post_id)){
		return array($img_url, $arr_size['width'], $arr_size['height'], false);
	}
	return false;
}
add_filter('image_downsize', 'lb_image_downsize', 10, 3);

function lb_image_url($size = 'medium', $post_id){
	$arr_size = get_image_size($size);
	if($arr_size && $img_url = wp_get_attachment_url($post_id)){
		if('gif' == strtolower(substr($img_url,-3))){
			return $img_url;
		}
		$width_str = sprintf('w%s', $arr_size['width']);
		$suffix = '';
		switch ($size) {
			case FB_COVER_SIZE_NAME:
				$width_str = 'fb';
				$suffix = '/cover.png';
				break;
			case 'low-quality':
				$width_str = sprintf('wl%s', $size['width']);
				break;
			default:
				break;
		}
		$parts = parse_url($img_url);
		return sprintf('%s://%s/%s%s%s', $parts['scheme'], $parts['host'], $width_str, $parts['path'], $suffix);
	}
	return false;
}