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What should I do if I run into a CAPTCHA while web crawling?

2023-08-14 13:25

When performing web crawling, you sometimes run into CAPTCHA challenges, which can complicate and make automated data collection difficult. CAPTCHA are designed to distinguish between machines and humans to prevent malicious crawlers and bots from abusing websites. However, encountering CAPTCHA can be an obstacle when you need to perform legitimate data capture. In this article, we will discuss the strategies and solutions you should adopt when encountering CAPTCHA during web crawling.


I. Types of CAPTCHA


CAPTCHA, as a technique used to identify whether a user is a real human being, exists in several types, each of which requires the user to perform different tasks. The following are some common types of CAPTCHA:


1. Image CAPTCHA: The user is required to identify and select a specific image, e.g., an image containing a specific object or color in a set of images.


2. Text CAPTCHA: The user needs to recognize and enter text or numbers displayed in an image. The text may be distorted, skewed or have distracting lines to prevent the automated program from recognizing it.


3. Slider CAPTCHA: The user needs to drag a slider to mimic human sliding behavior. This type of CAPTCHA is usually used to recognize if the user is able to mimic real human actions.


4. Sound CAPTCHA: The user is required to listen to a sound being played and enter the text heard, usually used to assist visually impaired users.


5. Logic CAPTCHA: Users are asked to answer simple logic questions, such as solving a simple math problem or choosing a logical option.


6. Jigsaw CAPTCHA: Users are required to put a picture back together in its original form, usually by dragging and dropping the pieces of the picture into the correct position.


7. Arithmetic CAPTCHA: Users need to answer a simple arithmetic question, such as adding or multiplying two numbers.


II.Strategies for solving CAPTCHA


When you encounter a CAPTCHA in a web crawl, there are several strategies you can try to solve the problem:


a. Use a CAPTCHA recognition tool:

CAPTCHA recognition tools are automated techniques that recognize image or text CAPTCHAs. These tools are based on machine learning and image processing algorithms that can help you crack CAPTCHAs automatically, but are not always 100 percent accurate.


b. Human intervention:

Sometimes, the most reliable method is to have a human perform the CAPTCHA recognition. You can integrate a human intervention step in your automation script where the system asks the user to manually enter the CAPTCHA when it is encountered. This ensures accurate CAPTCHA recognition, but adds labor costs and operational complexity.


c. Use of proxies:

Using a proxy server, especially an overseas residential proxy, allows you to change the IP address of your request to potentially avoid restrictions on your access to a particular website. This may help to bypass some IP-based CAPTCHA restrictions.


d. Adjust the frequency of requests:

Some websites limit high frequency requests under the same IP address. By adjusting the frequency of requests, you can reduce the risk of being recognized as a bot and thus reduce the chances of encountering a CAPTCHA.


III. The role of residential proxies in solving CAPTCHA on websites


1. IP Diversity: Using a residential proxy can provide multiple real residential IP addresses, which makes each request seem to come from a different user rather than the same IP. this can help users avoid some of the defense mechanisms against frequent requests, as each IP has its own request frequency.


2. Reduce the risk of blocking: Some websites may identify frequent requests from the same IP as bots or malicious programs and take measures to block them. Using a residential proxy prevents a single IP from being blocked, thus reducing the risk of being blocked by a website.


3. CAPTCHA DISTRIBUTION: In some cases, frequent requests for CAPTCHA from the same IP within a short period of time may raise alarm as it may suggest bot activity. Residential proxies can reduce the likelihood of raising alarms by distributing requests to different IP addresses and avoiding multiple requests for CAPTCHA within a short period of time.


4. Handling Challenging CAPTCHA: Some websites use more complex CAPTCHA, such as image CAPTCHA or slider CAPTCHA. Residential agents can simulate real human actions, making it easier to handle these challenging CAPTCHA.


5. Reduce response times: Residential proxies typically have low latency, which is important in situations where a quick response to a CAPTCHA validation is required because if the response time is too long, the site may assume the user is a robot.


6. Circumvention of blocking: Some websites may have some means of recognizing proxy IP and blocking them, but IP from residential proxies are usually not easily recognized as proxies because they come from real residential networks.




CAPTCHA can be a challenge in web crawling, but they are not insurmountable. By using CAPTCHA recognition tools, human intervention, proxies, and other strategies, you can solve the CAPTCHA problem in a legal manner. But always remember that it's important to respect the rules and ethics of your website and make sure that your web crawling activities are legal and ethical.

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