<?php
/**
 * Writes the given text with a border into the image using TrueType fonts.
 * @author John Ciacia
 * @param image An image resource
 * @param size The font size
 * @param angle The angle in degrees to rotate the text
 * @param x Upper left corner of the text
 * @param y Lower left corner of the text
 * @param textcolor This is the color of the main text
 * @param strokecolor This is the color of the text border
 * @param fontfile The path to the TrueType font you wish to use
 * @param text The text string in UTF-8 encoding
 * @param px Number of pixels the text border will be
 * @see http://us.php.net/manual/en/function.imagettftext.php
 */
function imagettfstroketext(&$image, $size, $angle, $x, $y, &$textcolor, &$strokecolor, $fontfile, $text, $px) {

    for($c1 = ($x-abs($px)); $c1 <= ($x+abs($px)); $c1++)
        for($c2 = ($y-abs($px)); $c2 <= ($y+abs($px)); $c2++)
            $bg = imagettftext($image, $size, $angle, $c1, $c2, $strokecolor, $fontfile, $text);

   return imagettftext($image, $size, $angle, $x, $y, $textcolor, $fontfile, $text);
}

<?php
$img = imagecreatefrompng("/home/john/Desktop/test.png");
$font_color = imagecolorallocate($img, 0, 0, 0);
$stroke_color = imagecolorallocate($img, 255, 0, 0);
imagettfstroketext($img, 10, 0, 10, 50, $font_color, $stroke_color, "abstract.ttf", "Hello, World!", 2);
?>