wp_restore_image( int $post_id )

function wp_restore_image($post_id) {
	$meta = wp_get_attachment_metadata($post_id);
	$file = get_attached_file($post_id);
	$backup_sizes = $old_backup_sizes = get_post_meta( $post_id, '_wp_attachment_backup_sizes', true );
	$restored = false;
	$msg = new stdClass;

	if ( !is_array($backup_sizes) ) {
		$msg->error = __('Cannot load image metadata.');
		return $msg;
	}

	$parts = pathinfo($file);
	$suffix = time() . rand(100, 999);
	$default_sizes = get_intermediate_image_sizes();

	if ( isset($backup_sizes['full-orig']) && is_array($backup_sizes['full-orig']) ) {
		$data = $backup_sizes['full-orig'];

		if ( $parts['basename'] != $data['file'] ) {
			if ( defined('IMAGE_EDIT_OVERWRITE') && IMAGE_EDIT_OVERWRITE ) {

				// Delete only if it's an edited image.
				if ( preg_match('/-e[0-9]{13}\./', $parts['basename']) ) {
					wp_delete_file( $file );
				}
			} elseif ( isset( $meta['width'], $meta['height'] ) ) {
				$backup_sizes["full-$suffix"] = array('width' => $meta['width'], 'height' => $meta['height'], 'file' => $parts['basename']);
			}
		}

		$restored_file = path_join($parts['dirname'], $data['file']);
		$restored = update_attached_file($post_id, $restored_file);

		$meta['file'] = _wp_relative_upload_path( $restored_file );
		$meta['width'] = $data['width'];
		$meta['height'] = $data['height'];
	}

	foreach ( $default_sizes as $default_size ) {
		if ( isset($backup_sizes["$default_size-orig"]) ) {
			$data = $backup_sizes["$default_size-orig"];
			if ( isset($meta['sizes'][$default_size]) && $meta['sizes'][$default_size]['file'] != $data['file'] ) {
				if ( defined('IMAGE_EDIT_OVERWRITE') && IMAGE_EDIT_OVERWRITE ) {

					// Delete only if it's an edited image.
					if ( preg_match('/-e[0-9]{13}-/', $meta['sizes'][$default_size]['file']) ) {
						$delete_file = path_join( $parts['dirname'], $meta['sizes'][$default_size]['file'] );
						wp_delete_file( $delete_file );
					}
				} else {
					$backup_sizes["$default_size-{$suffix}"] = $meta['sizes'][$default_size];
				}
			}

			$meta['sizes'][$default_size] = $data;
		} else {
			unset($meta['sizes'][$default_size]);
		}
	}

	if ( ! wp_update_attachment_metadata( $post_id, $meta ) ||
		( $old_backup_sizes !== $backup_sizes && ! update_post_meta( $post_id, '_wp_attachment_backup_sizes', $backup_sizes ) ) ) {

		$msg->error = __('Cannot save image metadata.');
		return $msg;
	}

	if ( !$restored )
		$msg->error = __('Image metadata is inconsistent.');
	else
		$msg->msg = __('Image restored successfully.');

	return $msg;
}