oui c'est ça merci

        imagealphablending($im, FALSE);
        imagesavealpha($im, TRUE);

function imagecreatefromany($filepath) {
    $type = exif_imagetype($filepath);
    $allowedTypes = array(1, 2, 3, 6, 18); // gif, jpg, png, bmp, webp
    if (!in_array($type, $allowedTypes)) return false;
    switch ($type) {
        case 1 :
            $im = imagecreatefromgif($filepath);
        break;
        case 2 :
            $im = imagecreatefromjpeg($filepath);
        break;
        case 3 :
            $im = imagecreatefrompng($filepath);
        break;
        case 6 :
            $im = imagecreatefrombmp($filepath);
        break;
        case 18 :
            $im = imagecreatefromwebp($filepath);
        break;
    }   
    return $im; 
} 

$im = imagecreatefrompng('example.png');
$size = min(imagesx($im), imagesy($im));
$im2 = imagecrop($im, ['x' => 0, 'y' => 0, 'width' => $size, 'height' => $size]);
if ($im2 !== FALSE) {
    imagepng($im2, 'example-cropped.png');
    imagedestroy($im2);
}
imagedestroy($im);