upload.php

<?php
header("content-type: text/plain");

$images_dir_name = "images";
$ip = $_SERVER["REMOTE_ADDR"];

// machine dirs
$script_filedir = dirname($_SERVER["SCRIPT_FILENAME"]);
$image_save_dir = $images_dir_name . DIRECTORY_SEPARATOR . $ip;
define("SAVE_DIR", $script_filedir . DIRECTORY_SEPARATOR . $image_save_dir);

// http resources
$upload_dir = dirname($_SERVER["REQUEST_URI"]);
$image_res_dir = $images_dir_name . "/" . $ip;
$host = $_SERVER["HTTP_HOST"];
define("RESOURCE_DIR", "http://" . $host . $upload_dir . "/" . $image_res_dir);

function get_filename(){
    if(!file_exists(SAVE_DIR)){
        mkdir(SAVE_DIR);
    }

    $tempname = tempnam(SAVE_DIR, "i");

    return basename($tempname, ".tmp") . ".png";
}

function upload($tmp_file){
    $filename = get_filename();
    $new_path = SAVE_DIR . DIRECTORY_SEPARATOR . $filename;

    if(move_uploaded_file($tmp_file, $new_path)){
        return RESOURCE_DIR . "/" . $filename;
    }

    throw new Exception("failed to upload.");
}

echo upload($_FILES["imagedata"]["tmp_name"]);
?>