wp_get_attachment_url() working but wp_get_attachment_image() not working

Hi folks,

I am trying to make a widget which takes post id as input from user and displays images of the specified post in sidebar. wp_get_attachment_url()gets me the url but in the next line wp_get_attachment_image()doesn’t work on same photo=>id. I don’t know where I am going wrong.

Sharing the code of the widget I am tried to put together after going through other wordpress support group posts:

function widget( $args, $instance ) {
         echo $args['before_widget'];
    $photos = get_children( array('post_parent' => $instance['post'], 'post_type' => 'attachment', 'post_mime_type' => 'image') );

    //for getting inline post images only
    $post_id=$instance['post'];
    $content_post = get_post($post_id);
    $content = $content_post->post_content;
    $content = apply_filters('the_content', $content);
    $content = str_replace(']]>', ']]>', $content);

    if (!empty($photos)) :
        //Loop through each attachment..

        foreach ($photos as $photo_id => $photo) :
            //getting inline post images only
            $url = wp_get_attachment_url($photo_id);
            $position = strpos($content, $url);

            if($position){
                echo $post_id;
                //working
                echo wp_get_attachment_url($photo_id);
                //not working
                wp_get_attachment_image($photo_id, 'thumbnail') ;
            }
        endforeach ;
    endif ;