Insert image in WordPress with HTML5 <figure> tag and caption

functions.php

<?php
// Don't include the opening tag

function html5_insert_image( $html, $id, $caption, $title, $align, $url, $size, $alt ) {
  $src  = wp_get_attachment_image_src( $id, $size, false );
  $html5 = "<figure id=\"post-$id media-$id\" class=\"align-$align\">";

  if ( $url ) {
    $html5 .= "<a href=\"$url\" class=\"image-link\"><img src=\"$src[0]\" alt=\"$alt\" /></a>";
  } else {
    $html5 .= "<img src=\"$src[0]\" alt=\"$alt\" />";
  }

  if ( $caption ) {
    $html5 .= "<figcaption>$caption</figcaption>";
  }

  $html5 .= "</figure>";
  return $html5;
}
add_filter( 'image_send_to_editor', 'html5_insert_image', 10, 9 );

Adds two figure tags when there is a caption.

No good here at all! If you try to remove image from editor FIGURE tags are not deleted.