How to remove base URL from this statement?

I made this statement especially for ensuring a thumbnail gets posted on Facebook when my links are shared but because I use a CDN the thumbnails never appear. I want to make this query without the base url so then I can just use my normal url without the CDN so I can guarantee thumbnails will work on FB.

All helps is highly appreciated.

# Displays post image attachment for FB (sizes: thumbnail, medium, full)
function fb_attachment_image($postid=0, $size='thumbnail', $attributes='') {
	if ($postid<1) $postid = get_the_ID();
	if ($images = get_children(array(
		'post_parent' => $postid,
		'post_type' => 'attachment',
		'numberposts' => 1,
		'post_mime_type' => 'image',)))
		foreach($images as $image) {
			$attachment=wp_get_attachment_image_src($image->ID, $size);
			?><?php echo $attachment[0]; ?><?php
		}
}

Thanks in advance.