Academics Just Formalized "Reverse CAPTCHAs" — Here's a Working Open-Source Implementation

Earlier this month, a research team published aCAPTCHA — the first academic formalization of a question nobody was asking five years ago: "Is this entity an AI agent?" Not "is this a human?" — the opposite. The Problem: Verifying Agents, Not Blocking Them Traditional CAPTCHAs exist to prove you're human. But as AI agents become legitimate web participants — browsing, booking, purchasing, automating — a new need has emerged: some systems need to verify that a visitor is a bot. Think about it: Agent-only APIs that shouldn't serve human traffic AI-to-AI marketplaces where humans have no business being Multi-agent orchestration platforms requiring authenticated agents Agent-facing services that need to distinguish real agents from scripts The aCAPTCHA paper formalizes this as the Agentic Capability Verification Problem (ACVP). They define a three-class taxonomy — Human, Script, Agent — based on three capability dimensions: action, reasoning, and memory. The ke