Source

File: wp-includes/post.php

function wp_delete_attachment_files( $post_id, $meta, $backup_sizes, $file ) {
	global $wpdb;

	$uploadpath = wp_get_upload_dir();
	$deleted    = true;

	if ( ! empty( $meta['thumb'] ) ) {
		// Don't delete the thumb if another attachment uses it.
		if ( ! $wpdb->get_row( $wpdb->prepare( "SELECT meta_id FROM $wpdb->postmeta WHERE meta_key = '_wp_attachment_metadata' AND meta_value LIKE %s AND post_id <> %d", '%' . $wpdb->esc_like( $meta['thumb'] ) . '%', $post_id ) ) ) {
			$thumbfile = str_replace( wp_basename( $file ), $meta['thumb'], $file );

			if ( ! empty( $thumbfile ) ) {
				$thumbfile = path_join( $uploadpath['basedir'], $thumbfile );
				$thumbdir  = path_join( $uploadpath['basedir'], dirname( $file ) );

				if ( ! wp_delete_file_from_directory( $thumbfile, $thumbdir ) ) {
					$deleted = false;
				}
			}
		}
	}

	// Remove intermediate and backup images if there are any.
	if ( isset( $meta['sizes'] ) && is_array( $meta['sizes'] ) ) {
		$intermediate_dir = path_join( $uploadpath['basedir'], dirname( $file ) );

		foreach ( $meta['sizes'] as $size => $sizeinfo ) {
			$intermediate_file = str_replace( wp_basename( $file ), $sizeinfo['file'], $file );

			if ( ! empty( $intermediate_file ) ) {
				$intermediate_file = path_join( $uploadpath['basedir'], $intermediate_file );

				if ( ! wp_delete_file_from_directory( $intermediate_file, $intermediate_dir ) ) {
					$deleted = false;
				}
			}
		}
	}

	if ( ! empty( $meta['original_image'] ) ) {
		if ( empty( $intermediate_dir ) ) {
			$intermediate_dir = path_join( $uploadpath['basedir'], dirname( $file ) );
		}

		$original_image = str_replace( wp_basename( $file ), $meta['original_image'], $file );

		if ( ! empty( $original_image ) ) {
			$original_image = path_join( $uploadpath['basedir'], $original_image );

			if ( ! wp_delete_file_from_directory( $original_image, $intermediate_dir ) ) {
				$deleted = false;
			}
		}
	}

	if ( is_array( $backup_sizes ) ) {
		$del_dir = path_join( $uploadpath['basedir'], dirname( $meta['file'] ) );

		foreach ( $backup_sizes as $size ) {
			$del_file = path_join( dirname( $meta['file'] ), $size['file'] );

			if ( ! empty( $del_file ) ) {
				$del_file = path_join( $uploadpath['basedir'], $del_file );

				if ( ! wp_delete_file_from_directory( $del_file, $del_dir ) ) {
					$deleted = false;
				}
			}
		}
	}

	if ( ! wp_delete_file_from_directory( $file, $uploadpath['basedir'] ) ) {
		$deleted = false;
	}

	return $deleted;
}