functions.php

<?php

/**
 * Customize Gallery Metabox Image Output
 *
 * @param string $output
 * @param string $image_url
 * @param object $image, post object
 * @return string $output
 */
function be_new_image_markup( $output, $image_url, $image ) {
  
  $output = '<img src="' . $image_url . '" alt="' . esc_attr( $image->post_title ) . '" rel="' . esc_attr( $image->ID ) . '" title="' . esc_attr( $image->post_content ) . '" /> ';
  return $output;

}
add_filter( 'be_gallery_metabox_output', 'be_new_image_markup', 10, 3 );