You have to write custom code to get the attachment id and post_parent by **name**/ **slug** or **filename**(if it has not been changed during the uploading of files).

Put the below code in your theme's **functions.php** file

    if( ! ( function_exists( 'wp_get_attachment_by_post_name' ) ) ) {
	    function wp_get_attachment_by_post_name( $post_name ) {
		    	$args           = array(
		    		'posts_per_page' => 1,
		    		'post_type'      => 'attachment',
		    		'name'           => trim( $post_name ),
		    	);

		    	$get_attachment = new WP_Query( $args );

		    	if ( ! $get_attachment || ! isset( $get_attachment->posts, $get_attachment->posts[0] ) ) {
		    		return false;
		    	}

		    	return $get_attachment->posts[0];
	    }
    }

then you can call the function where you need it like below :--

    $attachment = wp_get_attachment_by_post_name( $post_name );
    // Replace post_name by the name/slug of the attachment
    // It will give you an object, which you can render like below to get the ID and post_parent
    if ( $attachment ) {
        echo $attachment->ID; // Gives the id of the attachment
        echo $attachment->post_parent; // Gives the post_parent id
        echo $attachment->post_title; // Gives the attachment title.
    }