Overcoming CAPTCHAs When Web Scraping with PHP

Web scraping can be a useful technique for collecting data from websites. However, many sites use CAPTCHAs (Completely Automated Public Turing test to tell Computers and Humans Apart) to prevent scraping by bots. In this guide, we'll explore methods for handling CAPTCHAs when scraping with PHP.

What is a CAPTCHA and Why Do Sites Use Them?

A CAPTCHA is a type of challenge-response test used to determine if a user is human. They often involve reading distorted text or identifying images. CAPTCHAs aim to block bots and scrapers while allowing human users through.

Sites use CAPTCHAs to prevent abuse of their services. For example, mass ticket purchases from a ticketing site or sending spam from a webmail provider. CAPTCHAs can be annoying for legitimate human users, but remain an effective bot deterrent.

Approaches for Bypassing CAPTCHAs When Scraping

When you encounter CAPTCHAs while scraping, there are a few approaches you can try:

Use a CAPTCHA Solving Service

Several online services offer human and machine-learning powered CAPTCHA solving for a fee. They provide an API you can send the CAPTCHA image or audio to and get back the solved response. This allows you to incorporate CAPTCHA solving into your scraper code.

Some popular CAPTCHA solving services to check out include Anti-Captcha and DeathByCaptcha.

Here's an example using Anti-Captcha's API:

$client = new AntiCaptchaClient("your_api_key");

$captcha_image_base64 = file_get_contents($captcha_url); 

$solved_text = $client->solveCaptcha($captcha_image_base64);

Use a Browser Automation Tool

Browser automation tools like Selenium allow you to programmatically drive a real web browser. This means CAPTCHAs can be solved manually or using image recognition within the browser session.

The approach would be:

1. Load the target page in the browser using Selenium
2. Detect when the CAPTCHA appears
3. Bring it into focus and solve it manually or with image recognition
4. Resume the scraping script after the CAPTCHA is solved

Here's some sample Selenium + PHP code:

// start chrome browser via Selenium 
$driver = new ChromeDriver(); 

// load target page
$driver->get('http://example.com');

// solve captcha logic would go here...

// get page source to scrape
$html = $driver->getPageSource();

The main downside to this method is it doesn't scale well unless you create a browser farm, which is complex to set up.

Use a Proxy Service

Some proxy services rotate IP addresses with each request, making it appear you are a normal human visitor. This allows you to bypass sites that lock out scraping from a single IP after too many requests.

Scraping through proxies can result in getting around CAPTCHAs, but this tactic is becoming less effective over time as sites improve detection.

Ethical Considerations for CAPTCHA Solving

While there are methods for defeating CAPTCHAs, it raises some ethical concerns to consider:

I'd recommend reaching out to a site owner before scraping protected data at excess scale. There may be an official API or data offering available instead.

Scraping public data at reasonable volumes is usually fine. Just be sure to fly under the radar and not trigger IP locks or abuse alerts.

Key Takeaways for Handling CAPTCHAs When Scraping

Here are the main tips to remember:

With the right approach and precautions, it is possible to overcome CAPTCHAs for web scraping projects. The methods discussed provide options to responsibly scrape sites employing protections.