<?php

function fileExists($fileName, $caseSensitive = true) {
    //echo $fileName;die();
    if(file_exists($fileName)) {
        return $fileName;
    }
    if($caseSensitive) return false;

    // Handle case insensitive requests            
    $directoryName = dirname($fileName);
    $fileArray = glob($directoryName . '/*', GLOB_NOSORT);
    $fileNameLowerCase = strtolower($fileName);
    foreach($fileArray as $file) {
        if(strtolower($file) == $fileNameLowerCase) {
            return $file;
        }
    }
    return false;
}

$the_file_name = fileExists($_GET['img'], false);
header('Content-Type: image/jpg');
readfile($the_file_name);