Protect a generate image with php

I'm having a problem here and I think people here can help me.

I have a file that generates an image, ler.php, and the f开发者_运维知识库ile that loads the images through a while, carregar.php.

I need to block direct access to the images generated by ler.php, tried to make a system like this session:

carregar.php:

<?
$_session['a'] = 1;
while($a != 50) { echo "<img src='ler.php?imagem=$a'>"; $a++; }
$_session['a'] = 0;
?>

ler.php:

<? if($_session['a'] == 1) { //load image } ?>

The result is the only loading the first image.

I'm trying to now use the $_SERVER ["PHP_SELF"], placing the IF of ler.php, what happens is I load it through <img src=''> she identifies as carregar.php.

Who has the best solution? I've tried several ways with $_SESSION and it seems to not really work.

I could suggest two ways:

1. Easy to implement, less protective: in ler.php check that $_SERVER["HTTP_REFERER"] refers to "carregar.php".

2. A little bit more complicated: in carregar.php generate an unique code for each image you're going to output and store it in $_SESSION. Then pass the code to ler.php as a GET parameter. In ler.php check if the code exists in $_SESSION object, then generate an image and remove the code from $_SESSION.

I have a hard time identifying the problem, but your use of the session is going to lead to unexpected results:

You are adding 50 (I guess...) image tags to a page and right after you have added these tags, you set the session variable to 0.

The browser only loads a few files from the same server at the same time, so when the script is done and the first image is loaded, the browser is going to request the next image but that will fail as you have set the session variable to 0 already.

The only way to reliably set the session variable to 0 after all images have loaded, is an ajax request from your page that checks and triggers after all images have completely loaded.

Good! I managed to resolve one way and improvised without using AJAX:

ler.php:

<?php
    if(isset($_SERVER["HTTP_REFERER"])) {
    $check2 = (strpos($_SERVER["HTTP_REFERER"], 'carregar.php') > 0) ? true : false;
    if(print_r($check2) != 11) {
// Blank
    }
    } else {          
    if(isset($_SERVER["HTTP_REFERER"]))
    {
// Load Image
    }
    if(!isset($_SERVER["HTTP_REFERER"]))
    {
// Blank
    }
?>

So, the image only can be loaded into my page. Maybe...