/*

         * Edited by Omer Barlas

         * Original: $preview=get_post_meta($post->ID, 'preview_value', true);

         */

        if (has_post_thumbnail($post->ID)) {

            $image_src = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID));

            if (is_array($image_src)) {

                $preview = $image_src[0];

            } else {

                $preview = false;

            }

        } else {

            $preview = get_post_meta($post->ID, 'preview_value', true);

        }