класс изменения размера изображения.

$maxsize = 100;
$image="img.jpg";
$size = GetImageSize($image); 
$width = $size[0]; 
$height = $size[1]; 
$x_ratio = $maxsize / $width; 
$y_ratio = $maxsize / $height; 
if ( ($width <= $maxsize) && ($height <= $maxsize) ) { 
  $tn_width = $width;       
  $tn_height = $height; 
} 
else if (($x_ratio * $height) < $maxsize) { 
  $tn_height = ceil($x_ratio * $height); 
  $tn_width = $maxsize; 
} 
else { 
  $tn_width = ceil($y_ratio * $width); 
  $tn_height = $maxsize; 
} 
$src = ImageCreateFromJpeg($image); 
$dst = ImageCreateTrueColor($tn_width,$tn_height); 
ImageCopyResized($dst, $src, 0, 0, 0, 0, 
    $tn_width,$tn_height,$width,$height); 
header("Content-type: image/jpeg"); 
ImageJpeg ($dst, null, 40);
ImageDestroy($src); 
ImageDestroy($dst);