This is an optimised and bug fixed version of nojer at yahoo dot com's rotatedellipse function. I've changed it so that the arguments are compatible with imageellipse. See notes on imagearc for original version.

<?php

function rotatedellipse($im, $cx, $cy, $width, $height, $rotateangle, $colour, $filled=false) {
  // modified here from nojer's version
  // Rotates from the three o-clock position clockwise with increasing angle.
  // Arguments are compatible with imageellipse.

  $width=$width/2;
  $height=$height/2;

  // This affects how coarse the ellipse is drawn.
  $step=3;

  $cosangle=cos(deg2rad($rotateangle));
  $sinangle=sin(deg2rad($rotateangle));

  // $px and $py are initialised to values corresponding to $angle=0.
  $px=$width * $cosangle;
  $py=$width * $sinangle;
  
  for ($angle=$step; $angle<=(180+$step); $angle+=$step) {
    
    $ox = $width * cos(deg2rad($angle));
    $oy = $height * sin(deg2rad($angle));
    
    $x = ($ox * $cosangle) - ($oy * $sinangle);
    $y = ($ox * $sinangle) + ($oy * $cosangle);
 
    if ($filled) {
      triangle($im, $cx, $cy, $cx+$px, $cy+$py, $cx+$x, $cy+$y, $colour);
      triangle($im, $cx, $cy, $cx-$px, $cy-$py, $cx-$x, $cy-$y, $colour);
    } else {
      imageline($im, $cx+$px, $cy+$py, $cx+$x, $cy+$y, $colour);
      imageline($im, $cx-$px, $cy-$py, $cx-$x, $cy-$y, $colour);
    }
    $px=$x;
    $py=$y;
  }
}

function triangle($im, $x1,$y1, $x2,$y2, $x3,$y3, $colour) {
   $coords = array($x1,$y1, $x2,$y2, $x3,$y3);
   imagefilledpolygon($im, $coords, 3, $colour);
}

?>

if you want to display an ellipse in the upper left corner of an image, you can easily calculate the corresponding cx and cy values. this example will draw an ellipse having the same width and height as the image.

<?php

$ellipse_width = 100;
$ellipse_height = 200;

$ellipse_cx = ($ellipse_width / 2);
$ellipse_cy = ($ellipse_height / 2);

$img_x = $ellipse_width;
$img_y = $ellipse_height;

$img = imagecreate($img_x, $img_y);
$bg = imagecolorallocate($img, 255,255,255);

$ellipse_color = imagecolorallocate($img, 0, 0, 0);

imageellipse($img, $ellipse_cx, $ellipse_cy, $ellipse_width, $ellipse_height, $ellipse_color);

header("Content-type: image/png");
imagepng($img);
imagedestroy($img);

?>

When you wana use "ImageEllipse" function 
in under GD 2.0.2 version, you can use "ImageArc" like bellow

----------------------------------------------------
$file_name = "test.png";

$screen_x = 300;
$screen_y = 200;

$x1 = $screen_x / 2;
$y1 = $screen_y / 2;

$radius = 30;

$image = ImageCreate($screen_x, $screen_y);
$black = ImageColorAllocate($image, 0,0,0);

ImageArc($image, $x1, $y1, $radius , $radius , 0, 360, $black);

ImagePng($image, $file_name); 
ImageDestroy($image); 
----------------------------------------------------