You state that people shouldn't rely on the MIME type passed along with the uploaded file, because it is not checked for authenticity and can be forged, but have no qualms with 'trusting' the file extension?

Also, using an alternative method, the extension can be grabbed with: $ext = pathinfo($filename, PATHINFO_EXTENSION);

Finally, to answer the original question posed by Orc, $_FILES[...]['name'] will contain the name of the file as sent by the browser (eg. myimage.jpg), extension and all.