It will involves in several reasons as follows:

Even with a proxy, your browser might leave identifiable traces that indicate automated behavior. Websites can detect Selenium through certain browser characteristics, such as the absence of specific browser features, or through known Selenium signatures like the presence of specific navigator properties (navigator.webdriver being true).

Bots often perform actions much faster or in more predictable patterns than human users. Rapid page navigation, uniform mouse movements, or consistently timed actions can signal to the server that your traffic is automated.

If the proxy isn't correctly configured, some requests (like WebSocket connections, AJAX calls, or resource loading) might bypass the proxy, exposing your real IP address or creating discrepancies that alert the server.

Many websites use CAPTCHA systems to block bots. If a CAPTCHA is triggered and not solved (or incorrectly solved by an automation tool), the server can flag the session as bot-driven.

Even with a proxy, if your scraping activities exceed normal user behavior in terms of request frequency or volume, or if the proxy IP has been previously flagged or blacklisted, the server may suspect bot activity.

Some websites run JavaScript checks to detect automation tools. Selenium may fail certain checks that browsers normally pass, such as rendering dynamic content, handling JavaScript popups, or responding to subtle mouse movements and clicks.

Modify the Selenium WebDriver to mask it more effectively, such as changing the user-agent string, disabling the navigator.webdriver property, and ensuring that the browser’s fingerprints closely match a legitimate browser. Mimic human behavior: Introduce randomness in your actions (e.g., mouse movements, scrolling, delays between actions) to appear more like a human user.

Regularly change your proxy IP and user-agent strings to reduce the likelihood of being detected as a bot. Slow down your requests: Avoid making too many requests in a short period. Use randomized delays to mimic human browsing behavior.

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If you encounter CAPTCHAs, consider using a service that can solve them automatically. These measures can help reduce the likelihood of your Selenium-driven scraper being detected as a bot, but they do not guarantee complete evasion, especially as detection techniques become more sophisticated.