Returns true if the file named by filename was uploaded via HTTP POST. This is useful to help ensure that a malicious user hasn't tried to trick the script into working on files upon which it should not be working--for instance, /etc/passwd.
This sort of check is especially important if there is any chance that anything done with uploaded files could reveal their contents to the user, or even to other users on the same system.
For proper working, the function is_uploaded_file needs an argument like $_FILES['userfile']['tmp_name'], - the name of the uploaded file on the client's machine $_FILES['userfile']['name'] does not work.
The filename being checked.
Returns true on success or false on failure.