tempnam()

[Anon]

If I use this function like as

$tmpfname = tempnam ("/tmp", "FOO");

$fp = fopen($tmpfname, "w");
fwrite($fp, "writing to tempfile");
fclose($fp);

the command automatically create a temp file yes, but the name on the filesystem is FOOxxxxx (where xxxxx are random chars).
How can I refet to this file if I need to use it in functions like as imagecopyresize where the filename is required?
Thanks