How to bypass 2chan captcha

Learn how to bypass 4chan's simple image CAPTCHA using 2Captcha API. Step-by-step guide with real code examples to automate CAPTCHA solving and form submission.

How to solve 4chan's text CAPTCHA using 2Captcha API

Some 4chan boards, especially when accessed via VPN or Tor, require solving a simple text CAPTCHA — an image with distorted letters or numbers. Unlike the slider puzzle, this one can be solved programmatically using 2Captcha.

Here’s a full guide to automate it.

Step 1 – Get the CAPTCHA image (base64)

On the page, locate the <img> tag showing the CAPTCHA:

<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUg..." />

Extract the base64 string:

const base64 = document.querySelector('img.captcha').src; // keep full data URI

✅ 2Captcha supports both formats:

• pure base64 without prefix (iVBORw0K...)
• or full data URI (data:image/png;base64,...)

Step 2 – Send the image to 2Captcha

Create a task using the ImageToTextTask type:

POST https://api.2captcha.com/createTask
Content-Type: application/json

{
  "clientKey": "YOUR_2CAPTCHA_API_KEY",
  "task": {
    "type": "ImageToTextTask",
    "body": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUg...",
    "phrase": false,
    "case": false,
    "numeric": 0,
    "math": false,
    "minLength": 4,
    "maxLength": 6
  },
  "languagePool": "en"
}

⚠️ Make sure the image is under 100kB and not larger than 1000x1000px.

Step 3 – Poll for the result

After creating the task, store the taskId, then call:

POST https://api.2captcha.com/getTaskResult

{
  "clientKey": "YOUR_2CAPTCHA_API_KEY",
  "taskId": "PUT_TASK_ID_HERE"
}

Repeat this request every 3 seconds, starting 5 seconds after task creation.

Example of success response:

{
  "errorId": 0,
  "status": "ready",
  "solution": {
    "text": "K7aQ9"
  }
}

Step 4 – Submit the CAPTCHA

Insert the solution into the form:

document.querySelector('input[name="captcha_response"]').value = "K7aQ9";

Then trigger the form submission as usual.

Optional: Report incorrect CAPTCHA

If 4chan rejects the answer (false negative), you can report the task:

POST https://api.2captcha.com/reportIncorrectResult

{
  "clientKey": "YOUR_2CAPTCHA_API_KEY",
  "taskId": "PUT_TASK_ID_HERE"
}

Summary

This technique helps you post automatically to 4chan when the standard CAPTCHA is used. If you're facing the slider puzzle, this guide won't work — it's a different, more advanced system.