$caption_image_count = 0;

function count_images(){
    global $post;
    $thePostID = $post->ID;
    $parameters = array(
        'post_type' => 'attachment',
        'post_parent' => $thePostID,
        'post_mime_type' => 'image');
    $attachments = get_children($parameters);
    $content = count($attachments);
    return $content;
}
#add_filter('the_content','count_images');

function caption_image_callback($matches) {
    global $caption_image_count;
    $caption_image_count += 1;
    $c = count_images();
    for ($i=1; $i <= $c; $i++) {
        if (is_single()) {
            return '<div class="inum"><span align="center">' . $caption_image_count . '</span></div><div align="left">
            <img src="'.$matches[2].'"'.$matches[3].'></div>';
        } else {
            return '<img src="'.$matches[2].'"'.$matches[3].'>';
        }
    }
}

function caption_image($post_body_content) {
    global $caption_image_count;
    $post_body_content = preg_replace_callback("|<img(.*?)src=\"(.*?)\"(.*?)>|","caption_image_callback",$post_body_content);
    $caption_image_count = 0;
    return $post_body_content;
}

if ( current_user_can('edit_plugins') ) {
    add_filter('the_content', 'caption_image'); }