This function will resize any input file restricting the width and height to be no more than the specified pixels, and output a binary stream.
function resize_jpg($inputFilename, $new_side){
$imagedata = getimagesize($inputFilename);
$w = $imagedata[0];
$h = $imagedata[1];
if ($h > $w) {
$new_w = ($new_side / $h) * $w;
$new_h = $new_side;
} else {
$new_h = ($new_side / $w) * $h;
$new_w = $new_side;
}
$im2 = ImageCreateTrueColor($new_w, $new_h);
$image = ImageCreateFromJpeg($inputFilename);
imagecopyResampled ($im2, $image, 0, 0, 0, 0, $new_w, $new_h, $imagedata[0], $imagedata[1]);
return $im2;
}