function saveImage($inPath, $outPath)
{
    $in  = fopen($inPath, "rb");
    $out = fopen($outPath, "wb");
    while ($chunk = fread($in, 8192)) {
        fwrite($out, $chunk, 8192);
    }
    fclose($in);
    fclose($out);
}

saveImage('https://hcti.io/v1/image/a123e292-a54b-4df0-915f-8a07ea49e8ce', 'image.jpg');