$url = 'http://www.tibia.com/logging/url'; // The URL to the accountmanagement page
$f1 = 'accnr'; // Name of field1(ON THE WEBSITE YOU'RE TRYING TO LOGIN ON!)
$f2 = 'pass'; // Name of field2(ON THE WEBSITE YOU'RE TRYING TO LOGIN ON!)
$v1 = $_POST['acc']; // Value of field1(FROM THE WEBSITE YOU'RE TRYING TO LOGIN FROM!)
$v2 = $_POST['pw']; // Value of field2(FROM THE WEBSITE YOU'RE TRYING TO LOGIN FROM!)
$find = 'Welcome to your account'; // String to search for in the page you've logged in on
$postchars = http_build_query( array($f1 => $v1, $f2 => $v2) );

$stream = stream_context_create( array('http' => array('method' => 'POST', 'header'  => 'Content-Type: application/x-www-form-urlencoded', 'content' =>  htmlspecialchars_decode( $postchars ) ) ) ); // Creates an array of the sourcecode, and inputs the values of the field1 and field2

$content = file_get_contents($url, false, $stream); // Gets the sourcecode from the new page that is loaded after the input of the values.

$search = strpos($content, $find); // Search the sourcecode for the specific string in the variable "find"

if($search === false){
echo 'The login seems to be incorrect. Please try again, or check if you have a valid account';
} // If the string wasn't found
else {
echo 'Your account is valid!';
}  // If the string was found