Create captcha in php

3 Steps Simple Captcha In PHP (Free Download)

Welcome to a tutorial on how to create a simple captcha in PHP. Have a website that is constantly being spammed by angry keyboard warriors? Time to put in some security and prevention measures. Let us walk through an example in this guide, without the use of any 3rd party frameworks – Read on!

TABLE OF CONTENTS

PHP CAPTCHA

All right, let us now get into the details of creating a simple PHP captcha.

STEP 1) PHP CAPTCHA CLASS

 if (session_status()==PHP_SESSION_NONE) < session_start(); >> // (C) PRIME THE CAPTCHA - GENERATE RANDOM STRING IN SESSION function prime () : void < $char = "abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; $max = strlen($char) - 1; $_SESSION["captcha"] = ""; for ($i=0; $ilength; $i++) < $_SESSION["captcha"] .= substr($char, rand(0, $max), 1); >> // (D) DRAW THE CAPTCHA IMAGE function draw ($mode=0) : void < // (D1) FUNKY BACKGROUND IMAGE if (!isset($_SESSION["captcha"])) < exit("Captcha not primed"); >$captcha = imagecreatetruecolor($this->capW, $this->capH); list($bx, $by) = getimagesize($this->capB); $bx = ($bx-$this->capW) < 0 ? 0 : rand(0, ($bx-$this->capW)); $by = ($by-$this->capH) < 0 ? 0 : rand(0, ($by-$this->capH)); imagecopy($captcha, imagecreatefromjpeg($this->capB), 0, 0, $bx, $by, $this->capW, $this->capH); // (D2) RANDOM TEXTBOX POSITION $ta = rand(-20, 20); // random angle $tc = imagecolorallocate($captcha, rand(120, 255), rand(120, 255), rand(120, 255)); // random text color $ts = imagettfbbox($this->capFS, $ta, $this->capF, $_SESSION["captcha"]); if ($ta>=0) < $tx = rand(abs($ts[6]), $this->capW - (abs($ts[2]) + abs($ts[6]))); $ty = rand(abs($ts[5]), $this->capH); > else < $tx = rand(0, $this->capW - (abs($ts[0]) + abs($ts[4]))); $ty = rand(abs($ts[7]), abs($ts[7]) + $this->capH - (abs($ts[3]) + abs($ts[7]))); > imagettftext($captcha, $this->capFS, $ta, $tx, $ty, $tc, $this->capF, $_SESSION["captcha"]); // (D3) OUTPUT CAPTCHA if ($mode==0) < ob_start(); imagepng($captcha); $ob = base64_encode(ob_get_clean()); echo ""; > else < header("Content-type: image/png"); imagepng($captcha); imagedestroy($captcha); >> // (E) VERIFY CAPTCHA function verify ($check) < if (!isset($_SESSION["captcha"])) < exit("Captcha not primed"); >if ($check == $_SESSION["captcha"]) < unset($_SESSION["captcha"]); return true; >else < return false; >> > // (F) CAPTCHA OBJECT $PHPCAP = new Captcha();

First, we start with the “core engine”, the Captcha library. Yes, this looks complicated at first, but keep calm and explore it slowly.

• (A) A whole bunch of captcha settings. Feel free to change to your own font, change the background, captcha image dimensions, etc…
• (B & F) When $PHPCAP = new Captcha() is created, the constructor automatically starts the session if it is not already started.
• (C To E) There are only 3 “real captcha functions”.
  • prime() Step 1 of the process, pretty much just generates a random string into $_SESSION[«captcha»] .
  • draw() Step 2 of the process, use this to output the HTML captcha image.
  • verify() When the user submits the form, use this to verify the user’s captcha against the session.

  STEP 2) GENERATE CAPTCHA IN HTML FORM

  Name Email Are you human? prime(); $PHPCAP->draw(); ?>

  

  1. The “usual form fields”.
  2. Generate the captcha.
     • Captain Obvious to the rescue, require «1-captcha.php» to load the library.
     • Call the $PHPCAP->prime() function to generate a random captcha string into the session.
     • Call the $PHPCAP->draw() function to generate the captcha image.

  STEP 3) CAPTCHA VERIFICATION UPON SUBMISSION

  verify($_POST["captcha"])) < $result = "Congrats, CAPTCHA is correct."; print_r($_POST); >// (C) NOPE else

  On submitting the form, we only need to use $PHPCAP->verify($_POST[«captcha»]) to check if the user has entered the correct captcha – Proceed if the challenge passed, or show an error message if it failed.

  DOWNLOAD & NOTES

  Here is the download link to the example code, so you don’t have to copy-paste everything.

  SUPPORT

  600+ free tutorials & projects on Code Boxx and still growing. I insist on not turning Code Boxx into a «paid scripts and courses» business, so every little bit of support helps.

  EXAMPLE CODE DOWNLOAD

  Click here for the source code on GitHub gist, just click on “download zip” or do a git clone. I have released it under the MIT license, so feel free to build on top of it or use it in your own project.

  EXTRA BITS & LINKS

  That’s all for the code, and here are a few small extras that may be useful to you.

  MORE SECURITY

  Before the “security experts” start to bang on their keyboards, some additional security can be added to this simple captcha.

  • Impose a time limit/expiry on the captcha, 10 minutes for example – $_SESSION[«cexpire»] = strtotime(«now») + 600 .
  • Change the verify() function to also do a time check – if ($_SESSION[«cexpire»] > strototime(«now»)) < NOPE >.
  • Add a number of times a user can challenge the captcha. Decide what to do if the challenge fails too many times – Maybe require the user to click on an email verification link.
  • Very simply, use HTTPS.

  RELOADING THE CAPTCHA

  • “Move” the captcha creation to a separate mycap.php script – prime(); $PHPCAP->draw();
  • Modify 2-form.php , replace the captcha with an empty
  • Use Javascript fetch to load/reload the captcha.
    • var cap = () => fetch(«mycap.php»).then(res=>res.text()).then(txt=>document.getElementById(«cap»).innerHTML = txt);
    • window.addEventListener(«load», cap);

    LINKS & REFERENCES

    • PHP Sessions (Very Simple Examples) – Code Boxx
    • GD Image Library – PHP
    • Changed your mind? Want something better? Check out the free Google reCaptcha.
    • Simple PHP Contact Form With Google reCaptcha – Code Boxx

    THE END

    Thank you for reading, and we have come to the end of this guide. I hope that it has helped you to better fight spam in your project, and if you want to share anything with this guide, please feel free to comment below. Good luck and happy coding!

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