Source

File: wp-admin/includes/image-edit.php

function wp_restore_image( $post_id ) {
	$meta             = wp_get_attachment_metadata( $post_id );
	$file             = get_attached_file( $post_id );
	$backup_sizes     = get_post_meta( $post_id, '_wp_attachment_backup_sizes', true );
	$old_backup_sizes = $backup_sizes;
	$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;
}