Source

File: wp-includes/class-wp-image-editor-imagick.php

public function flip( $horz, $vert ) {
		try {
			if ( $horz ) {
				$this->image->flipImage();
			}

			if ( $vert ) {
				$this->image->flopImage();
			}

			// Normalise EXIF orientation data so that display is consistent across devices.
			if ( is_callable( array( $this->image, 'setImageOrientation' ) ) && defined( 'Imagick::ORIENTATION_TOPLEFT' ) ) {
				$this->image->setImageOrientation( Imagick::ORIENTATION_TOPLEFT );
			}
		} catch ( Exception $e ) {
			return new WP_Error( 'image_flip_error', $e->getMessage() );
		}

		return true;
	}