get images attached to post

It’s better to use get_children than get_posts. Here is a quick example that will work. This is in the form of a function that is defined in your plugin or in functions.php then use the function as a template tag.

    /**
     * Gets all images attached to a post
     * @return string
     */
    function wpse_get_images() {
        global $post;
        $id = intval( $post->ID );
        $size="medium";
        $attachments = get_children( array(
                'post_parent' => $id,
                'post_status' => 'inherit',
                'post_type' => 'attachment',
                'post_mime_type' => 'image',
                'order' => 'ASC',
                'orderby' => 'menu_order'
            ) );
        if ( empty( $attachments ) )
                    return '';

        $output = "\n";
    /**
     * Loop through each attachment
     */
    foreach ( $attachments as $id  => $attachment ) :

        $title = esc_html( $attachment->post_title, 1 );
        $img = wp_get_attachment_image_src( $id, $size );

        $output .= '<a class="selector thumb" href="' . esc_url( wp_get_attachment_url( $id ) ) . '" title="' . esc_attr( $title ) . '">';
        $output .= '<img class="aligncenter" src="' . esc_url( $img[0] ) . '" alt="' . esc_attr( $title ) . '" title="' . esc_attr( $title ) . '" />';
        $output .= '</a>';

    endforeach;

        return $output;
    }