by Alessia Amelio (University of Calabria), Darko Brodić, Sanja Petrovska (University of Belgrade), Radmila Janković (Serbian Academy of Sciences and Arts)
“CAPTCHA Samples” is a new website for testing different types of CAPTCHA specifically designed for research and study purposes.
In recent decades, the CAPTCHA test has received much attention owing to the increasing security problems affecting the web, for which risk prevention plays a key role. CAPTCHA is an acronym of “Completely Automated Public Turing Test to tell Computers and Humans Apart”. This is a test program which an internet user is required to solve in order to prove that he or she is human and thus gain access to a given website. In fact, the CAPTCHA test is designed to be easily solved by a human and difficult to solve for an automatic program which tries to obtain unauthorized access to the website . Recently, different types of CAPTCHA have flourished in the literature, with more sophisticated security mechanisms that guarantee efficacy in risk prevention, and more user-friendly interfaces , . In order for researchers to effectively build on the recent work in this area, an analysis of the most recently introduced CAPTCHA tests is needed.
Accordingly, we present CAPTCHA Samples, a new website collecting different CAPTCHA tests for research and analysis purposes. CAPTCHA Samples, available at [L1] (see Figure 1), was born as a joint project involving the Technical Faculty in Bor, University of Belgrade, Serbia, and DIMES University of Calabria, Italy.
Figure 1: CAPTCHA Samples website.
Currently, the website reports different samples of image-based CAPTCHA tests, including tests based on facial expressions (animated characters, face of an old woman, surprised face, and worried face). The aim of these CAPTCHA tests is to recognise the correct image from a list of different images, according to the question asked by the test. From the homepage, it is possible to select the CAPTCHA test of interest and access to the corresponding webpage. The CAPTCHA test can be solved in order to obtain useful information about the usability of the test, including: (i) completion time, which is the solution time to the CAPTCHA, and (ii) number of tries to provide the correct solution to the CAPTCHA.
If the CAPTCHA test is not correctly solved, then the failure is notified by a text field of “wrong answer” on the screen, and the user is asked to try again. Otherwise, if the CAPTCHA test is correctly solved, a message in a text field on the screen is visualised, reporting the completion time and the number of tries to find the correct solution. Figure 2 shows an example of a successfully solved “surprised face” CAPTCHA test, which was solved in 2.48 seconds and one attempt.
Figure 2: Webpage of CAPTCHA Samples with a message reporting success in solving the test, including completion time and number of attempts.
Every test is completely anonymous because any personal information is registered about the internet user who accesses the CAPTCHA. Also, the main advantage of the website is that the CAPTCHA tests can be accessed from different devices, including smartphones, laptops and tablets. In this way, the difference in terms of CAPTCHA usability between multiple devices can be easily checked. In the future, we are planning to extend the CAPTCHA Samples website with new functionalities, including the selection of other CAPTCHA tests of different typology, which will be added to the website. It will be particularly useful in academic as well as industrial research for anonymously gathering data about the usability of CAPTCHA tests. It could also be the starting point for designing new CAPTCHA types which are appropriate for specific types of internet users. For more detailed information about the image-based CAPTCHA tests included in the CAPTCHA Samples website, please refer to .
 A.M. Turing: “Computing Machinery and Intelligence”, Mind 59:433-460, 1950.
 D. Brodić, S. Petrovska, M. Jevtić, Z. N. Milivojević: “The influence of the CAPTCHA types to its solving times”, MIPRO: 1274-1277, 2016.
 D. Brodić, A. Amelio, R. Janković: “Exploring the Influence of CAPTCHA Types to the Users Response Time by Statistical Analysis”, Multimedia Tools and Applications, 1-37, 2017.
Alessia Amelio, University of Calabria, Rende, Italy