$new_avatar_img = imagecreate(50,50);
$avatar_img = imagecreatefromjpeg($_FILES['avatar']['tmp_name']);
$width = $height = max(imagesx($avatar_img), imagesy($avatar_img));
imagecopyresized($new_avatar_img, $avatar_img, 0, 0, $width, $height, 50, 50, imagesx($avatar_img), imagesy($avatar_img));
imagejpeg($new_avatar_img, '/images/'.$_SESSION['username'].'.jpg' )