Source

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

public function maybe_exif_rotate() {
		$orientation = null;

		if ( is_callable( 'exif_read_data' ) && 'image/jpeg' === $this->mime_type ) {
			$exif_data = @exif_read_data( $this->file );

			if ( ! empty( $exif_data['Orientation'] ) ) {
				$orientation = (int) $exif_data['Orientation'];
			}
		}

		/**
		 * Filters the `$orientation` value to correct it before rotating or to prevemnt rotating the image.
		 *
		 * @since 5.3.0
		 *
		 * @param int    $orientation EXIF Orientation value as retrieved from the image file.
		 * @param string $file        Path to the image file.
		 */
		$orientation = apply_filters( 'wp_image_maybe_exif_rotate', $orientation, $this->file );

		if ( ! $orientation || 1 === $orientation ) {
			return false;
		}

		switch ( $orientation ) {
			case 2:
				// Flip horizontally.
				$result = $this->flip( true, false );
				break;
			case 3:
				// Rotate 180 degrees or flip horizontally and vertically.
				// Flipping seems faster and uses less resources.
				$result = $this->flip( true, true );
				break;
			case 4:
				// Flip vertically.
				$result = $this->flip( false, true );
				break;
			case 5:
				// Rotate 90 degrees counter-clockwise and flip vertically.
				$result = $this->rotate( 90 );

				if ( ! is_wp_error( $result ) ) {
					$result = $this->flip( false, true );
				}

				break;
			case 6:
				// Rotate 90 degrees clockwise (270 counter-clockwise).
				$result = $this->rotate( 270 );
				break;
			case 7:
				// Rotate 90 degrees counter-clockwise and flip horizontally.
				$result = $this->rotate( 90 );

				if ( ! is_wp_error( $result ) ) {
					$result = $this->flip( true, false );
				}

				break;
			case 8:
				// Rotate 90 degrees counter-clockwise.
				$result = $this->rotate( 90 );
				break;
		}

		return $result;
	}