Takayuki Miyoshi

Really Simple CAPTCHA does not work alone and is intended to work with other plugins. It is originally created for <a href="https://contactform7.com/" rel="nofollow ugc">Contact Form 7</a>, however, you can use it with your own plugin.
Note: This product is “really simple” as its name suggests, i.e., it is not strongly secure. If you need perfect security, you should try other solutions.
<h4>How does it work?</h4>
Really Simple CAPTCHA does not use PHP “Sessions” for storing states, unlike many other PHP CAPTCHA solutions, but stores them as temporary files. This allows you to embed it into WordPress without worrying about conflicts.
When you generate a CAPTCHA, Really Simple CAPTCHA creates two files for it; one is an image file of CAPTCHA, and the other is a text file which stores the correct answer to the CAPTCHA.
The two files have the same (random) prefix in their file names, for example, “a7hk3ux8p.png” and “a7hk3ux8p.txt.” In this case, for example, when the respondent answers “K5GF” as an answer to the “a7hk3ux8p.png” image, then Really Simple CAPTCHA calculates hash of “K5GF” and tests it against the hash stored in the “a7hk3ux8p.txt” file. If the two match, the answer is confirmed as correct.
<h4>How to use with your plugin</h4>
Note: Below are instructions for plugin developers.
First, create an instance of ReallySimpleCaptcha class:
<pre><code>$captcha_instance = new ReallySimpleCaptcha();
</code></pre>
You can change the instance variables as you wish.
<pre><code>// Change the background color of CAPTCHA image to black
$captcha_instance->bg = array( 0, 0, 0 );
</code></pre>
See really-simple-captcha.php if you are interested in other variables.
Generate a random word for CAPTCHA.
<pre><code>$word = $captcha_instance->generate_random_word();
</code></pre>
Generate an image file and a corresponding text file in the temporary directory.
<pre><code>$prefix = wp_rand();
$captcha_instance->generate_image( $prefix, $word );
</code></pre>
Then, show the image and get an answer from respondent.
Check the correctness of the answer.
<pre><code>$correct = $captcha_instance->check( $prefix, $the_answer_from_respondent );
</code></pre>
If the $correct is true, go ahead. Otherwise, block the respondent — as it would appear not to be human.
And last, remove the temporary image and text files, as they are no longer in use.
<pre><code>$captcha_instance->remove( $prefix );
</code></pre>
That’s all.
If you wish to see a live sample of this, you can try <a href="https://contactform7.com/captcha/" rel="nofollow ugc">Contact Form 7</a>.

Really Simple CAPTCHA

Needed this for an installation with custom forms. I used the plugin developers instructions and was able to make a fully custom implementation based on server side validation within 30 minutes. No more spam bots misusing the forms. Thank you!

Great work - easy to implement

Really Simple CAPTCHA is a CAPTCHA module intended to be called from other plugins. It is originally created for my Contact Form 7 plugin.

Costel Tudose

Protect your Contact Form 7 forms with Google CAPTCHA V2, hCAPTCHA or Cloudflare Turnstile CAPTCHA
Easy integration and supports multiple forms on a single page.
<h3>Google reCAPTCHA V2</h3>
Use <a href="https://www.google.com/recaptcha/admin" rel="nofollow ugc">https://www.google.com/recaptcha/admin</a> to generate Site key and Secret key.
When generating keys, choose Challenge (v2) -> “I’m not a robot” Checkbox
Update Site key and Secret key from Settings => Contact Form 7 Captcha => Google reCAPTCHA
To add reCAPTCHA V2 protection, insert [cf7sr-recaptcha] shortcode above the submit button in your Contact Form 7 form.
Default size of reCaptcha is normal, for compact size use shortcode: [cf7sr-recaptcha size=”compact”] 
Default color theme of reCaptcha is light, for dark theme use shortcode: [cf7sr-recaptcha theme=”dark”] 
Default type of reCaptcha is image, for audio type use shortcode: [cf7sr-recaptcha type=”audio”] 
You can combine multiple attributes, sample shortcode: [cf7sr-recaptcha size=”compact” theme=”dark”] 
You can also force reCaptcha to render in a specific language.
<h3>hCAPTCHA</h3>
Use <a href="https://dashboard.hcaptcha.com/signup" rel="nofollow ugc">https://dashboard.hcaptcha.com/signup</a> to generate Site key and Secret key.
Update Site key and Secret key from Settings => Contact Form 7 Captcha => hCAPTCHA
To add hCAPTCHA protection, insert [cf7sr-hcaptcha] shortcode above the submit button in your Contact Form 7 form.
Default size of hCAPTCHA is normal, for compact size use shortcode: [cf7sr-hcaptcha size=”compact”] 
Default color theme of hCAPTCHA is light, for dark theme use shortcode: [cf7sr-hcaptcha theme=”dark”] 
You can combine multiple attributes, sample shortcode: [cf7sr-hcaptcha size=”compact” theme=”dark”] 
You can also force hCAPTCHA to render in a specific language.
<h3>Cloudflare Turnstile CAPTCHA</h3>
Use <a href="https://www.cloudflare.com/en-gb/products/turnstile/" rel="nofollow ugc">https://www.cloudflare.com/en-gb/products/turnstile/</a> to generate Site key and Secret key.
Update Site key and Secret key from Settings => Contact Form 7 Captcha => Cloudflare Turnstile Captcha
To add Cloudflare Turnstile CAPTCHA protection, insert [cf7sr-turnstile] shortcode above the submit button in your Contact Form 7 form.
Default size of CAPTCHA is normal, for compact size use shortcode: [cf7sr-turnstile size=”compact”] 
Default color theme of CAPTCHA is auto, for light or dark theme use shortcode: [cf7sr-turnstile theme=”light”] or [cf7sr-turnstile theme=”dark”] 
You can combine multiple attributes, sample shortcode: [cf7sr-turnstile size=”compact” theme=”dark”] 
You can also force CAPTCHA to render in a specific language.

Contact Form 7 Captcha

Add reCAPTCHA V2, hCAPTCHA or Cloudflare Turnstile CAPTCHA to Contact Form 7

Really Simple CAPTCHA vs Contact Form 7 Captcha