Validate captcha with PHP

Question

I have a captcha in a form where an image with 5 randomly generated values is displayed. How do I validate the captcha and only send the contact if the input value is equal to the one generated by the image?

Excerpt from the form that has the captcha:

<div class="col one-fourth" style="padding: 0 3px;">
    <img src="captcha.php"/>
</div>
<div class="col one-fourth" style="padding: 0 3px;">
    <input type="text" name="captcha" id="captcha" placeholder="Digite o código ao lado" class="campos_form" maxlength="5" required/>
</div>

This is the file I call that generates the image with captcha:

<?php
session_start();
$codigoCaptcha = substr(md5( time()) ,0,5);
$_SESSION['captcha'] = $codigoCaptcha;

$imagemCaptcha = imagecreatefrompng("imagens/fundocaptcha.png");
$fonteCaptcha = imageloadfont("anonymous.gdf");
$corCaptcha = imagecolorallocate($imagemCaptcha,46,139,87);

imagestring($imagemCaptcha,$fonteCaptcha,15,5,$codigoCaptcha,$corCaptcha);
header("Content-type: image/png");
imagepng($imagemCaptcha);
imagedestroy($imagemCaptcha);
?>

How do I check if the user entered correctly? I can use the $_SESSION['captcha'] to compare the value? And how do I capture the value of input?

Answer 1

Hello,

can yes, capture the input value using

// pode ser feito assim...
$captchaEnviado = $_POST['captcha'];

//ou assim... que é mais seguro...
$captchaEnviado = filter_input(INPUT_POST, 'captcha', FILTER_SANITIZE_STRING);

if($captchaEnviado == $_SESSION['captcha'] ){
  //ok... continua...
}
else{
  //valor errado... trata como achar que deve....
}

more information on the filter_input here

and as mentioned in this right here in the O.R.