imagetypes() gives the image format and types supported by the current version of GD-PHP.
If we would like to pass values througn a form or an URL then we need to encode and to decode them using htmlspecialchars() and urlencode().
require() includes and evaluates a specific file, if the file is not found then it shows a Fatal Error.
require_once() includes only the file which is not being included before. It is used to be recommended for the files where you have lots of functions stored.
include() includes the file, even if the file is not found, but it gives a warning to the user to include().
Used to store variables of the current session.
The purpose of the function $_SESSION is to store data that you would like to preserve across page loads and to store variables of current session.
The mysql_fetch_array() function returns a row from a recordset as an associative array and a numeric array.
If two or more columns of the result have the same field names,then the last column will take precedence.