Add Credit URL to images and photos in WordPress

add_filter("attachment_fields_to_edit", "add_image_source_url", 10, 2);
function add_image_source_url($form_fields, $post) {
    $form_fields["source_url"] = array(
        "label" => __("Source URL"),
        "input" => "text",
        "value" => get_post_meta($post->ID, "source_url", true),
                "helps" => __("Add the URL where the original image was posted"),
    );
    return $form_fields;
}

add_filter("attachment_fields_to_save", "save_image_source_url", 10 , 2);
function save_image_source_url($post, $attachment) {
    if (isset($attachment['source_url']))
        update_post_meta($post['ID'], 'source_url', trim($attachment['source_url']));
    return $post;
}

add_filter('img_caption_shortcode', 'caption_shortcode_with_credits', 10, 3);
function caption_shortcode_with_credits($empty, $attr, $content) {
    extract(shortcode_atts(array(
        'id'    => '',
        'align' => 'alignnone',
        'width' => '',
        'caption' => ''
    ), $attr));

    // Extract attachment $post->ID
    preg_match('/\d+/', $id, $att_id);
    if (is_numeric($att_id[0]) && $source_url = get_post_meta($att_id[0], 'source_url', true)) {
        if (!strstr($source_url, 'http://'))
            $source_url = 'http://' . $source_url;
        $parts = parse_url($source_url);
        $caption .= ' ('. __('via') .' <a href="'. $source_url .'">'. $parts['host'] .'</a>)';
    }

    if ( 1 > (int) $width || empty($caption) )
        return $content;

    if ( $id )
        $id = 'id="' . esc_attr($id) . '" ';

    return '<div ' . $id . 'class="wp-caption ' . esc_attr($align) . '" style="width: ' . (10 + (int) $width) . 'px">'
    . do_shortcode( $content ) . '<p class="wp-caption-text">' . $caption . '</p></div>';
}