A simple image uploader in PHP

upload.php

<?php
/**
 * A simple image uploader
 * Federico Ponzi
 */
 
/*  Config: **/
// Base url, for the json response:
define ("BASE_URL", "http://127.0.0.1/");
// Where to put the images:
define ("UPLOADS_DIR", "uploads/");
//Max filesize in bytes:
define ("MAX_FILESIZE", "500000");

$response['status'] = "error";

/**
 * @return True, if the file is an image
 */
function isImage()
{
        $target_file = $_FILES["fileToUpload"]["tmp_name"];
        $check = getimagesize($target_file);
        $image_type = $check[2];

        if(in_array($image_type , array(IMAGETYPE_GIF , IMAGETYPE_JPEG ,IMAGETYPE_PNG , IMAGETYPE_BMP)))
        {
                return true;
        }
        return false;
}

/**
 * @return true if the file is too big
 */
function fileTooBig()
{
        return $_FILES["fileToUpload"]["size"] > MAX_FILESIZE;
}

/**
 * It returns a unique random file (based on the files list in UPLOADS_DIR
 */
function getUniqueName($fileName)
{
        while(file_exists(UPLOADS_DIR . $fileName)) 
        {
                $fileName = bin2hex(openssl_random_pseudo_bytes(10)) . $fileName;
        //Generate random name.
        }
        return $fileName;
}

//The main script:
if(isset($_FILES['fileToUpload']["name"]))
{
        if(!isImage())
        {
                $response['error'] = "Wrong file type error.";
        }
        else if(fileTooBig())
        {
                $response['error'] = "The image is too big.";

        }

        else if (!move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], ($fileName = UPLOADS_DIR . getUniqueName(basename($_FILES["fileToUpload"]["name"]))))) {
                $response['error'] = "Can't complete the upload due to a Server error."; 
        }
        else
        {
                $response['status'] = "ok";
                $response['path'] = BASE_URL . UPLOADS_DIR . $fileName;
        }
}
else
{
    $response['error'] = "No file uploaded.";
}

header('Content-Type: application/json');
echo json_encode($response);
?>