how to check require found the file in php code example

Example 1: php check if file exists

if (!file_exists('http://mysite.com/images/thumbnail_1286954822.jpg')) {   
$filefound = '0';                         
}

Example 2: php check if folder exists

<?php
$filename = '/path/to/foo.txt';

if (file_exists($filename)) {
    echo "The file $filename exists";
} else {
    echo "The file $filename does not exist";
}
?>