This is how i do it:
$Temp_Dump = $_FILES["file"]["tmp_name"];
// Get new sizes
list($width, $height) = getimagesize($Temp_Dump);
$newwidth = 90;
$newheight = 90;
// Load
$Temp_thumb = imagecreatetruecolor($newwidth, $newheight);
//$source = imagecreatefromjpeg($Temp_Dump);
if($extension == "jpg" OR $extension=='jpeg'){
$source = ImageCreateFromJpeg($Temp_Dump);
}elseif ($extension == "gif"){
$source = ImageCreateFromGIF($Temp_Dump);
}elseif ($extension == 'png'){
$source = imageCreateFromPNG($Temp_Dump);
}
// Resize
imagecopyresized($Temp_thumb, $source, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);