php random image file name

try using the php uniqid method to generate the unique id you need

$RandomAccountNumber = uniqid();
move_uploaded_file($ProfilePicTemp, "Content/" . $RandomAccountNumber);

When I upload images, I usually save it as the sha1() of the image's contents (sha1_file()). That way, you get two birds with one stone: You'll never (if you do, go fill out the closest lottery) get duplicate file names, AND, you'll prevent duplicate images (because duplicate images would have the same checksum).

Then, you have a database to sort out which image is which, and correctly display them to the user.

This is what I use when uploading pictures: a combination of session_id(), time() and a random string:

$rand = genRandomString();
$final_filename = $rand."_".session_id()."_".time();

function genRandomString() 
    $length = 5;
    $characters = "0123456789ABCDEFGHIJKLMNOPQRSTUVWZYZ";

    $real_string_length = strlen($characters) ;     

    for ($p = 0; $p < $length; $p++) 
        $string .= $characters[mt_rand(0, $real_string_length-1)];

    return strtolower($string);

I hope this help.