使用 PHP 创建图像验证码

Question

Hi i want to create a image captcha with php , i have the next code for my form.

<form action="" method="POST">
    <div class="label_form">Usuario:</div> <input type="text" name="user"/><br>
    <div class="label_form">Contraseña:</div> <input type="password" name="pass"/><br>  
    <img alt="Numeros aleatorios" src="layouts/captcha.php" />  
    <input class="label_form" type="text" name="num"/><br>
    <input type="submit" value="ENTRAR" name="submit"/>
</form> 

This is the code for validation before to send the form:

if (isset($_POST["submit"])) {
  if ($_SESSION['img_number'] != $_POST['num']) {
    echo "<div class='msg_error'>Los caracteres no se corresponden.</div>";
  } else {
    /*DO STUFF*/
  }
}

And in other file with the name captcha.php i have the code php for generate the image:

header("Content-type: image/png");
$string = "abcdefghijklmnopqrstuvwxyz0123456789";
for ($i = 0; $i < 5; $i++) {
  $pos = rand(0, 36);
  $str. = $string {
    $pos
  };
}
$img_handle = ImageCreate(60, 22) or die("Es imposible crear la imagen");
$back_color = ImageColorAllocate($img_handle, 102, 102, 153);
$txt_color = ImageColorAllocate($img_handle, 255, 255, 255);
ImageString($img_handle, 31, 5, 0, $str, $txt_color);
Imagepng($img_handle);
session_start();
$_SESSION['img_number'] = $str;

This give a image broken showing the alt from img "Numeros aleatorios" , so that tell me the file.php is calling fine the img but the code for generated is not working, any help is gratefull :D thanks.

Answer 1

Try changing:

$str .= $string{$pos};

to

$str .= $string[$pos]; //Array of strings.

I've updated my answer:

<?php
header("Content-type: image/png");
$string = "abcdefghijklmnopqrstuvwxyz0123456789"; 
for ($i = 0; $i < 5; $i++) { 
    $pos = rand(0,36); 
    $str .= $string[$pos]; 
}
$img_handle = ImageCreate (60, 22) or die ("Es imposible crear la imagen"); 
$back_color = ImageColorAllocate($img_handle,102,102,153); 
$txt_color = ImageColorAllocate($img_handle,255,255,255); 
ImageString($img_handle, 31, 5, 0, $str, $txt_color); 
Imagepng($img_handle); 
session_start(); 
$_SESSION['img_number'] = $str;
?>

In my local server the captcha image is showing properly.

Answer 2

Your code is good the only thing you missed is declaring $str = "" at the top of your catpcha.php file

Here is a working capture of your code:

Update

Your $string length is 36, so you should generate a random position between 0 and 35, like this:

$pos = rand(0,35);

If not, you sometimes get a broken image and a PHP Notice.

Update N°2

The reason why you get a broken image without declaring $str = "" is because this line

$str .= $string{$pos};

Throws a PHP Notice and corrupts the image. (Of course only if you display_errors , that's why it worked perfectly for @Danny's server)

Answer 3

Use this code in captacha.php, You can try this:

<?php
@session_start();
header("Content-type: image/png");
$_SESSION["captcha"] = substr(md5(time()),0,5);
$im = imagecreate(110, 30);
$white = imagecolorallocate($im, 244, 255, 255);
$red = imagecolorallocate($im, 255, 255, 255);
$black = imagecolorallocate($im, 0, 0, 0);
$size = $_SESSION["captcha"];
$text = "$size";
$font = 'comic.TTF';
imagettftext($im, 20, 0, 25, 20, $red, $font, $text);
imagettftext($im, 20, 0, 25, 20, $black, $font, $text);
imagepng($im);
imagedestroy($im);
?>

You need a font like comic.TTF for image font style.

More details about Captcha in PHP