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CAPTCHAs are widely used by websites to block bots and spam by presenting challenges that are easy for humans but difficult for automated programs to solve. To improve accessibility, audio CAPTCHAs are designed to complement visual ones.…

Sound · Computer Science 2026-01-14 Ziqi Ding , Yunfeng Wan , Wei Song , Yi Liu , Gelei Deng , Nan Sun , Huadong Mo , Jingling Xue , Shidong Pan , Yuekang Li

This paper studies how multimodal large language models (MLLMs) undermine the security guarantees of visual CAPTCHA. We identify the attack surface where an adversary can cheaply automate CAPTCHA solving using off-the-shelf models. We…

Cryptography and Security · Computer Science 2026-05-13 Junyu Wang , Changjia Zhu , Yuanbo Zhou , Lingyao Li , Xu He , Mingkui Wei , Junjie Xiong

As multimodal large language models (LLMs) advance, traditional CAPTCHAs have become obsolete at distinguishing humans from bots. To address this shift, this paper aims to investigate the possibility of using tasks for which humans have…

Cryptography and Security · Computer Science 2026-04-07 Choon-Hou Rafael Chong

Online services rely on CAPTCHAs as a first line of defense against automated abuse, yet recent advances in multi-modal large language models (MLLMs) have eroded the effectiveness of conventional designs that focus on text recognition or 2D…

Artificial Intelligence · Computer Science 2025-10-07 Arina Kharlamova , Bowei He , Chen Ma , Xue Liu

Benefiting from strong and efficient multi-modal alignment strategies, Large Visual Language Models (LVLMs) are able to simulate human visual and reasoning capabilities, such as solving CAPTCHAs. However, existing benchmarks based on visual…

Artificial Intelligence · Computer Science 2025-12-15 Jianyi Zhang , Ziyin Zhou , Xu Ji , Shizhao Liu , Zhangchi Zhao

To this date, CAPTCHAs have served as the first line of defense preventing unauthorized access by (malicious) bots to web-based services, while at the same time maintaining a trouble-free experience for human visitors. However, recent work…

Cryptography and Security · Computer Science 2020-11-05 Dorjan Hitaj , Briland Hitaj , Sushil Jajodia , Luigi V. Mancini

CAPTCHAs have become a ubiquitous tool in safeguarding applications from automated bots. Over time, the arms race between CAPTCHA development and evasion techniques has led to increasingly sophisticated and diverse designs. The latest…

Cryptography and Security · Computer Science 2024-05-14 Gelei Deng , Haoran Ou , Yi Liu , Jie Zhang , Tianwei Zhang , Yang Liu

CAPTCHAs are widely employed for distinguishing humans from automated bots online. However, current vision based CAPTCHAs face escalating security risks: traditional attacks continue to bypass many deployed CAPTCHA schemes, and recent…

Computers and Society · Computer Science 2025-12-19 Ziqi Ding , Shangzhi Xu , Wei Song , Yuekang Li

A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is an automatic security mechanism used to determine whether the user is a human or a malicious computer program. It is a program that generates and…

Human-Computer Interaction · Computer Science 2013-12-31 Mohammad Jabed Morshed Chowdhury , Narayan Ranjan Chakraborty

CAPTCHAs have been a critical bottleneck for deploying web agents in real-world applications, often blocking them from completing end-to-end automation tasks. While modern multimodal LLM agents have demonstrated impressive performance in…

Artificial Intelligence · Computer Science 2025-06-02 Yaxin Luo , Zhaoyi Li , Jiacheng Liu , Jiacheng Cui , Xiaohan Zhao , Zhiqiang Shen

The proliferation of the Internet and mobile devices has resulted in malicious bots access to genuine resources and data. Bots may instigate phishing, unauthorized access, denial-of-service, and spoofing attacks to mention a few.…

Cryptography and Security · Computer Science 2023-07-21 N. Tariq , F. A. Khan , S. A. Moqurrab , G. Srivastava

CAPTCHA is a human-centred test to distinguish a human operator from bots, attacking programs, or other computerised agents that tries to imitate human intelligence. In this research, we investigate a way to crack visual CAPTCHA tests by an…

Computer Vision and Pattern Recognition · Computer Science 2020-06-26 Zahra Noury , Mahdi Rezaei

CAPTCHAs are commonly used to distinguish between human and bot users on the web. However, despite having various types of CAPTCHAs, there are still concerns about their security and usability. To address these concerns, we surveyed over…

Cryptography and Security · Computer Science 2024-05-30 Arun Reddy , Yuan Cheng

CAPTCHA (Completely Automated Public Truing test to tell Computers and Humans Apart) is a widely used technology to distinguish real users and automated users such as bots. However, the advance of AI technologies weakens many CAPTCHA tests…

Machine Learning · Computer Science 2021-01-08 Rulin Shao , Zhouxing Shi , Jinfeng Yi , Pin-Yu Chen , Cho-Jui Hsieh

For a number of years, many websites have used CAPTCHAs to filter out interactions by bots. However, attackers have found ways to circumvent CAPTCHAs by programming bots to solve or bypass them, or even relay them for humans to solve. In…

Cryptography and Security · Computer Science 2017-04-11 Nasser Mohammed Al-Fannah

Completely Automated Public Turing Test To Tell Computers and Humans Apart (CAPTCHA) has been implemented on many websites to identify between harmful automated bots and legitimate users. However, the revenue generated by the bots has…

Cryptography and Security · Computer Science 2023-06-14 Rui Jin , Lin Huang , Jikang Duan , Wei Zhao , Yong Liao , Pengyuan Zhou

For nearly two decades, CAPTCHAs have been widely used as a means of protection against bots. Throughout the years, as their use grew, techniques to defeat or bypass CAPTCHAs have continued to improve. Meanwhile, CAPTCHAs have also evolved…

Cryptography and Security · Computer Science 2023-07-25 Andrew Searles , Yoshimichi Nakatsuka , Ercan Ozturk , Andrew Paverd , Gene Tsudik , Ai Enkoji

Over the last years, most websites on which users can register (e.g., email providers and social networks) adopted CAPTCHAs (Completely Automated Public Turing test to tell Computers and Humans Apart) as a countermeasure against automated…

Human-Computer Interaction · Computer Science 2015-12-18 Mauro Conti , Claudio Guarisco , Riccardo Spolaor

Completely Automated Public Turing tests to tell Computers and Humans Apart (CAPTCHAs) are a foundational component of web security, yet traditional implementations suffer from a trade-off between usability and resilience against AI-powered…

Cryptography and Security · Computer Science 2025-10-06 Ayda Aghaei Nia

Large Language Models (LLMs) have demonstrated an alarming ability to impersonate humans in conversation, raising concerns about their potential misuse in scams and deception. Humans have a right to know if they are conversing to an LLM. We…

Computation and Language · Computer Science 2024-12-23 Gilad Gressel , Rahul Pankajakshan , Yisroel Mirsky
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