Using the fb_og_image_additional filter on Facebook Open Graph, Google+ and Twitter Card Tags for WordPress

fb_og_image_additional.php

<?php

add_filter( 'fb_og_image_additional', 'extra_preview_images' );
function extra_preview_images( $fb_image_additional ) {
	//You could/should use your own logic to decide which images to return. This example only shows you the structure of the array you should return.
	if ( !is_array( $fb_image_additional ) ) {
		$fb_image_additional = array();
	}
	$fb_image_additional[] = array(
		'fb_image' => 'https://domain.com/wp-content/uploads/og_image2.jpg',
		'png_overlay' => true, //Overlay PNG
	);
	$fb_image_additional[] = array(
		'fb_image' => 'https://domain.com/wp-content/uploads/og_image3.jpg',
		'png_overlay' => false, //Do not overlay PNG
	);
	return $fb_image_additional;
}