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ALTCHA's effectiveness

This document is tailored for a non-technical audience, website owners and product managers evaluating ALTCHA as a potential replacement for reCAPTCHA or similar solutions.

ALTCHA, an open-source protocol and a JavaScript widget, aims to combat spam and abuse on websites and web applications. While it doesn’t boldly claim to eradicate all internet spam, it offers a privacy-focused tool adaptable to evolving needs.

ALTCHA’s approach

The core principle

ALTCHA diverges from traditional CAPTCHAs by adopting a different focus. Rather than solely aiming to differentiate humans from bots, ALTCHA’s primary goal is to reduce spam by introducing a layer of complexity. This complexity acts as a barrier for spammers and automated bots attempting to abuse systems.

Proof of work

ALTCHA leverages a mechanism known as Proof of Work (PoW) to authenticate and validate user interactions. PoW demands considerable computational effort from the user’s device to validate requests. This requirement presents a significant hurdle for unsophisticated bots lacking the technical capabilities or resources to meet the computational demands.

Economical hurdle for spammers

The computational effort needed to validate requests through PoW poses a substantial obstacle for spammers aiming to post messages at scale. Spending extensive time on a single website becomes an uneconomical strategy, deterring spammers effectively.

While PoW doesn’t eliminate all spam, it significantly reduces it by requiring software capability and computational effort. To further enhance spam capture rates, integrate ALTCHA PoW with the Spam Filter.

Introducing the Spam Filter

The new GDPR-compliant Spam Filter is the latest addition to ALTCHA’s security toolkit, adding an extra layer of complexity. This filter classifies incoming data using natural language processing and machine learning, effectively filtering out unsolicited messages. Additionally, it analyzes factors like end-users’ email and IP addresses to provide further insights.

Privacy and compliance considerations

Privacy-centric regulations such as GDPR complicate CAPTCHA usage due to reliance on cookies and fingerprinting, mandating user consent. Google’s reCAPTCHA, for instance, utilizes cookies, causing issues in compliance efforts.

GDPR and privacy

ALTCHA conforms to GDPR guidelines, ensuring compliance and privacy adherence. It operates as a cookie-less solution, respecting user privacy without relying on intrusive tracking mechanisms, and aligning seamlessly with privacy regulations.

Embracing automation

Traditional CAPTCHAs, tedious and time-consuming, pose hurdles for users, potentially leading to customer loss. ALTCHA, on the other hand, promotes automated systems’ integration and enhances user experience, crucial for business success.

Alignment with future technologies

ALTCHA does not impede automation but rather accommodates it. By minimizing spam from unsophisticated bots, it aligns with the evolving landscape of technology, where automation plays a pivotal role in internet interactions.

Simplifying user experience

By embracing automated systems, ALTCHA simplifies user interactions. This approach minimizes friction compared to traditional CAPTCHAs, leading to higher user satisfaction and smoother experiences.


ALTCHA PoW effectively combats automated spam across various scenarios, particularly in basic web interactions. However, additional measures may be necessary for comprehensive protection against complex abuse or human-generated spam. To address this challenge, integrating ALTCHA’s Spam Filter solution provides an effective means of filtering out sophisticated bots and human-generated spam, thereby bolstering overall security measures.

ALTCHA offers flexibility for server-side enhancements, allowing the integration of supplementary mechanisms like fingerprinting, email or phone verification, or server-based rate-limiting. This adaptability enables customization based on varying security needs and specific use-case scenarios.


In essence, ALTCHA’s strength lies in its focus on complexity rather than solely distinguishing between humans and bots. Its implementation of PoW effectively deters unsophisticated bots, respects user privacy, aligns with evolving technologies, and offers adaptability to cater to different security requirements.

To further enhance its effectiveness against sophisticated bots and human-generated spam, consider combining the PoW mechanism with ALTCHA’s Spam Filter, which preserves accessibility and privacy while significantly bolstering protection.