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CAPTCHAs or reverse Turing tests are real-time assessments used by programs (or computers) to tell humans and machines apart. This is achieved by assigning and assessing hard AI problems that could only be solved easily by human but not by…

Human-Computer Interaction · Computer Science 2014-02-05 A. K. B. Karunathilake , B. M. D. Balasuriya , R. G. Ragel

Completely Automated Public Turing Test To Tell Computers and Humans Apart (CAPTCHA) is a type of challenge-response test widely used in authentication systems. A well-known challenge it faces is the CAPTCHA farm, where workers are hired to…

Cryptography and Security · Computer Science 2023-12-19 Rui Jin , Yong Liao , Pengyuan Zhou

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

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

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

As automation bot technology and Artificial Intelligence is evolving rapidly, conventional human verification techniques like voice CAPTCHAs and knowledge-based authentication are becoming less effective. Bots and scrapers with Artificial…

Cryptography and Security · Computer Science 2025-11-12 Aditya Mitra , Sibi Chakkaravarthy Sethuraman , Devi Priya V S

CAPTCHAs are employed as a security measure to differentiate human users from bots. A new sound-based CAPTCHA is proposed in this paper, which exploits the gaps between human voice and synthetic voice rather than relays on the auditory…

Cryptography and Security · Computer Science 2013-06-13 Haichang Gao , Honggang Liu , Dan Yao , Xiyang Liu , Uwe Aickelin

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

A verification code is an automated test method used to distinguish between humans and computers. Humans can easily identify verification codes, whereas machines cannot. With the development of convolutional neural networks, automatically…

Cryptography and Security · Computer Science 2019-02-13 Dongliang Xu , Bailing Wang , XiaoJiang Du , Xiaoyan Zhu , zhitao Guan , Xiaoyan Yu , Jingyu Liu

The modern pervasiveness of large-scale deep neural networks (NNs) is driven by their extraordinary performance on complex problems but is also plagued by their sudden, unexpected, and often catastrophic failures, particularly on…

Machine Learning · Computer Science 2023-08-02 Sadhana Lolla , Iaroslav Elistratov , Alejandro Perez , Elaheh Ahmadi , Daniela Rus , Alexander Amini

A secure human identification protocol aims at authenticating human users to a remote server when even the users' inputs are not hidden from an adversary. Recently, the authors proposed a human identification protocol in the RSA Conference…

Cryptography and Security · Computer Science 2007-05-23 Hassan Jameel , Heejo Lee , Sungyoung Lee

As a widely deployed security scheme, text-based CAPTCHAs have become more and more difficult to resist machine learning-based attacks. So far, many researchers have conducted attacking research on text-based CAPTCHAs deployed by different…

Computer Vision and Pattern Recognition · Computer Science 2020-08-27 Chunhui Li , Xingshu Chen , Haizhou Wang , Yu Zhang , Peiming Wang

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

The rapid evolution of GUI-enabled agents has rendered traditional CAPTCHAs obsolete. While previous benchmarks like OpenCaptchaWorld established a baseline for evaluating multimodal agents, recent advancements in reasoning-heavy models,…

Machine Learning · Computer Science 2026-02-10 Jiacheng Liu , Yaxin Luo , Jiacheng Cui , Xinyi Shang , Xiaohan Zhao , Zhiqiang Shen

Previous work showed that reCAPTCHA v2's image challenges could be solved by automated programs armed with Deep Neural Network (DNN) image classifiers and vision APIs provided by off-the-shelf image recognition services. In response to…

Cryptography and Security · Computer Science 2021-04-09 Md Imran Hossen , Yazhou Tu , Md Fazle Rabby , Md Nazmul Islam , Hui Cao , Xiali Hei

In this paper, we propose to utilize Automated Machine Learning to adaptively search a neural architecture for deepfake detection. This is the first time to employ automated machine learning for deepfake detection. Based on our explored…

Computer Vision and Pattern Recognition · Computer Science 2021-08-13 Ping Liu , Yuewei Lin , Yang He , Yunchao Wei , Liangli Zhen , Joey Tianyi Zhou , Rick Siow Mong Goh , Jingen Liu

Deep neural networks need to make robust inference in the presence of occlusion, background clutter, pose and viewpoint variations -- to name a few -- when the task of person re-identification is considered. Attention mechanisms have…

Computer Vision and Pattern Recognition · Computer Science 2020-06-18 Jieming Zhou , Soumava Kumar Roy , Pengfei Fang , Mehrtash Harandi , Lars Petersson

GUI agents are rapidly shifting from multi-module pipelines to end-to-end, native vision-language models (VLMs) that perceive raw screenshots and directly interact with digital devices. Despite rapid progress on general GUI tasks, CAPTCHA…

Cryptography and Security · Computer Science 2026-03-26 Yuxi Chen , Haoyu Zhai , Chenkai Wang , Rui Yang , Lingming Zhang , Gang Wang , Huan Zhang

As autonomous AI agents increasingly populate the Internet, a novel security challenge arises: "Is this entity an AI agent?" It is a new entity-type verification problem with no established solution. We formalize the problem through a…

Cryptography and Security · Computer Science 2026-03-10 Zuyao Xu , Xiang Li , Fubin Wu , Yuqi Qiu , Lu Sun , FaSheng Miao

CAPTCHAs are a defense mechanism to prevent malicious bot programs from abusing websites on the Internet. hCaptcha is a relatively new but emerging image CAPTCHA service. This paper presents an automated system that can break hCaptcha…

Cryptography and Security · Computer Science 2022-03-08 Md Imran Hossen , Xiali Hei