Usted puede utilizar la función uniqid()
para generar un identificador único
/**
* Generate a unique ID
* @link http://www.php.net/manual/en/function.uniqid.php
* @param prefix string[optional] <p>
* Can be useful, for instance, if you generate identifiers
* simultaneously on several hosts that might happen to generate the
* identifier at the same microsecond.
* </p>
* <p>
* With an empty prefix, the returned string will
* be 13 characters long. If more_entropy is
* true, it will be 23 characters.
* </p>
* @param more_entropy bool[optional] <p>
* If set to true, uniqid will add additional
* entropy (using the combined linear congruential generator) at the end
* of the return value, which should make the results more unique.
* </p>
* @return string the unique identifier, as a string.
*/
function uniqid ($prefix = null, $more_entropy = null) {}
http://stackoverflow.com/questions/8551763/storing-image-data-in-mysql-and-naming-conventions/8551813#8551813 – Richard
Use 'uniqid()' nombrar el archivo permanente con 'move_uploaded_file() ' –