Get Image tag from content of post

You can either make use of get_children or get_posts or even WP_Query to get the the attached image ID’s to the current post

You can then use those ID’s to gt the attached image with wp_get_attachment_image()

Here is a basic idea that you can use in a widget or sidebar. (CAVEAT: Untested)

$args = array( 
    'post_type' => 'attachment', 
    'numberposts' => -1, 
    'post_status' => null, 
    'post_parent' => get_queried_object_id()
); 

$attachments = get_posts( $args ); 

if ( $attachments ) { 

    foreach ( $attachments as $attachment ) { 

        echo '<li>'; 
        echo wp_get_attachment_image( $attachment->ID, 'full' ); 
        echo  '<p>'; echo apply_filters( 'the_title', $attachment->post_title ); 
        echo '</p></li>'; 
    } 
}