<?php
declare(strict_types=1);

$image = imagecreate(2, 2);
$bg = imagecolorallocate($image, 255, 0, 255);
imagecolortransparent($image, $bg);
imagegif($image, "icon.gif");
$loaded = imagecreatefromgif("icon.gif");
var_dump(imagecolortransparent($loaded) >= 0);