I couldn't get the replacements from 'the dot thawk' or 'pilot' to work for some reason, so here's my own replacement. It uses ImageMagick; binary must be installed, and you may need to modify the search path. (I didn't use PHP's ImageMagick support for my own reasons.)

<?php
    /**
     * imagerotate()
     * Debian php5-gd packages do not include imagerotate() due to some convoluted reason.
     *
     * @param int $angle - same as PHP builtin function
     * @param $bgd_color - not implemented, apparently always #FFFFFF
     *
     * @return same as PHP builtin function
     */
    if ( !function_exists( 'imagerotate' ) ) {

        function imagerotate( $source_image, $angle, $bgd_color ) {

            $angle = 360-$angle; // GD rotates CCW, imagick rotates CW

            foreach ( array( '/usr/bin', '/usr/local/bin', '/opt/local/bin', '/sw/bin' ) as $path ) {

                if ( file_exists( $path . '/convert' ) ) {
                    $imagick = $path . '/convert';
                    if ( $path == '/opt/local/bin' ) {
                        $imagick = 'DYLD_LIBRARY_PATH="" ' . $imagick; // some kind of conflict with MacPorts and MAMP
                    }
                    break;
                }

            }

            if ( !isset( $imagick ) ) {

                //trigger_error( 'imagerotate(): could not find imagemagick binary, original image returned', E_USER_WARNING );
                return $source_image;

            }

            $file1 = '/tmp/imagick_' . rand( 10000,99999 ) . '.png';
            $file2 = '/tmp/imagick_' . rand( 10000,99999 ) . '.png';

            if ( @imagepng( $source_image, $file1 ) ) {

                exec( $imagick . ' -rotate ' . $angle . ' ' . $file1 . ' ' . $file2 );

                if ( file_exists( $file2 ) ) {

                    $new_image = imagecreatefrompng( $file2 );
                    unlink( $file1 );
                    unlink( $file2 );
                    return $new_image;

                } else {

                    //trigger_error( 'imagerotate(): imagemagick conversion failed, original image returned', E_USER_WARNING );
                    return $source_image;

                }

            } else {

                //trigger_error( 'imagerotate(): could not write to ' . $file1 . ', original image returned', E_USER_WARNING );
                return $source_image;

            }

        }

    }
?>