How to Save php Site From Spammers?

Nowdays, mostly all of the site/blog owners are frustrated because of spammers, they put spam/phishing links in comments and contact forms also, whenver our geneuine users using site they may face problem because of this.

Now let's see how we can implement this,

assets/images/captcha.php

<?php
session_start();
if(isset($_SESSION['captcha']))
{
   unset($_SESSION['captcha']); 
   //removing if captcha already set for session
}

$string1 = "abcdefghijklmnpqrstuvwxyz";
$string2 = "123456789";

$string = $string1.$string2;
//From these 2 random string will be generated
$string = str_shuffle($string);
$rand = substr($string,0,5);

$_SESSION['captcha']=$rand;
//setting new captcha string

/* Create an image in php */

$myimg = imagecreate(100, 30);
$background = imagecolorallocate($myimg, 199, 144, 225); // background color
$text_colour = imagecolorallocate ($myimg, 245, 245, 245);      // text color 
imagestring($myimg,12,25,8,$_SESSION['captcha'],$text_colour); // add captcha code in image 
header ("Content-type: image/png");
imagepng ($myimg); // displayed image createde
imagedestroy($myimg); // remove allocated memory. 

?>

Now on the login page just use one image tag with src as the path of captcha.php, and check the if captcha is valid using the session.

for example.

login-validate.php

<?php
session_start();
if(isset($_SESSION['captcha']))
{
  if($_SESSION['captcha'] == $_POST['captcha']){
    echo 'valid captcha';
  }
  else{
    echo 'Invalid captcha';
  }
    
}
else{
  echo 'Please complete captcha';
}


?>

Now you can easily integrate this code in all of your pages where you expect the input from users.