Diakritika textu vkládaného do obrázku

<?php

putenv('GDFONTPATH=' . realpath('.'));
iconv_set_encoding('internal_encoding', 'utf-8');

class SimpleImage {

    private $image;
    private $imageNew;
    private $image_type;
    private $font = './Arial.ttf';

    function __construct() {
    }

    function load($filename) {

        $image_info = getimagesize($filename);
        $this->image_type = $image_info[2];

        if ($this->image_type == IMAGETYPE_JPEG) {
            $this->image = imagecreatefromjpeg($filename);
        }
        elseif ($this->image_type == IMAGETYPE_GIF) {
            $this->image = imagecreatefromgif($filename);
        }
        elseif ($this->image_type == IMAGETYPE_PNG) {
            $this->image = imagecreatefrompng($filename);
        }
    }

    function save($filename, $image_type=IMAGETYPE_JPEG, $compression=80, $permissions=null) {

        if ($this->image_type == IMAGETYPE_JPEG) {
            imagejpeg($this->image, $filename, $compression);
        }
        elseif ($this->image_type == IMAGETYPE_GIF) {
            imagegif($this->imageNew, $filename);
        }
        elseif ($this->image_type == IMAGETYPE_PNG) {
            imagepng($this->imageNew, $filename);
        }
    }

    function getWidth() {
        return imagesx($this->image);
    }

    function getHeight() {
        return imagesy($this->image);
    }

    function vodotiskVpravoDole($string) {

        $width	= 10 * strlen($string) ;
        $height	= 14; //ImageFontHeight($this->font);
        $im 	= $this->image;
        $x      = $this->getWidth() - $width - 10;
        $y	= $this->getHeight() - $height - 10;

        $background_color 	= imagecolorallocate ($im, 255, 255, 255); //white background
        $text_color 		= imagecolorallocate ($im, 0, 0,0);//black text

        imagettftext($im, '14', '0', $x, $y, $text_color, $this->font, $string);
        $this->image = $im;
    }
}

if (isset($_POST['ulozit'])) {
    $image = new SimpleImage();
    $image->load($_FILES['obrazek']['tmp_name']);

    $image->vodotiskVpravoDole("příliš žluťoučký kůň");

    $image->save('new.jpg');
}
?>
<form action="" method="post" enctype="multipart/form-data" name="formular" >
    <fieldset>
        <legend>Vyberte fotografii</legend><br />
        <input type="file" name="obrazek" value="vloz_obr" />
    </fieldset><br />
    <input type="hidden" name="ulozit" value="ulozit" />
    <input type="submit" name="ulozit" value="ulozit" />
    <br />

</form>

<?php
if (is_file('new.jpg')) {
    echo "<img src=\"new.jpg\" title=\"test\" alt=\"test\" />";
}
?>