Random security image code

Hello guys

I wrote some codes for security image.

<?php
//Start the session so we can store what the security code actually is
session_start();

//Send a generated image to the browser
create_image();
exit();

function create_image()
{
    //Let's generate a totally random string using md5
    $md5_hash = md5(rand(0,999)); 
    //We don't need a 32 character long string so we trim it down to 5 
    $security_code = substr($md5_hash, 15, 5); 

    //Set the session to store the security code
    $_SESSION["security_code"] = $security_code;

    //Set the image width and height
    $width = 75;
    $height = 30; 

    //Create the image resource 
    $image = ImageCreate($width, $height);  

    //We are making three colors, white, black and gray
    $white = ImageColorAllocate($image, 255, 255, 255);
    $black = ImageColorAllocate($image, 0, 0, 0);
    $grey = ImageColorAllocate($image, 204, 204, 204);

    //Make the background black 
    ImageFill($image, 0, 0, $black); 

    //Add randomly generated string in white to the image
    ImageString($image, 6, 15, 7, $security_code, $white); 

    //Throw in some lines to make it a little bit harder for any bots to break 

    imageline($image, 0, 5, $width, 5, $grey); 
    imageline($image, 0, 25, $width, 25, $grey); 

 
 
    //Tell the browser what kind of file is come in 
    header("Content-Type: image/jpeg"); 

    //Output the newly created image in jpeg format 
    ImageJpeg($image);
   
    //Free up resources
    ImageDestroy($image);
}
?>

PHP:

Using :

$scode = $_POST["scode"];
if ($_COOKIE["security_code"] != $scode) {
echo "Error!"
}

PHP:

 

you should add a no-cache http header there so the users will get fresh images always.

 

You should randomize the lines, and the formatting of the text. Otherwise it's really easy to break