A poor man's var_dump for the image_send_to_editor() filter in Wordpress. Throw this in your functions.php file and add an image to your post to see what get's passed. Filter it however you want to return the image however you want.

show_img_vars.php

<?php

function show_img_vars($html, $id, $caption, $title, $align, $url, $size, $alt) {
  // round up all the variables that get passed so we can test them
  $vars = "html = $html\n";
  $vars .= "id = $id\n";
  $vars .= "caption = $caption\n";
  $vars .= "title = $title\n"; // this will end up blank no matter what
  $vars .= "align = $align\n";
  $vars .= "url = $url\n";
  $vars .= "size = $size\n";
  $vars .= "alt = $alt\n";

  // return the normal html output you would expect
  $return = $html . "\n";

  // add our ad-hoc var dump to the editor
  $return .= "<!-- args \n";
  $return .= $vars;
  $return .= "/args -->";

  return $return;
}

add_filter( 'image_send_to_editor', 'show_img_vars', 10, 9 );

?>