CAPTCHA Based on The Form of Letters

The internet has been playing an increasingly influential role in human daily life, with the availability of many web services such as email, search engines and social media such as Facebook, Twitter, and Snapchat. However, these are often threatened by attacks from computer programs such as bots. To address this issue, CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) was developed to distinguish between computer programs and human users. One of simplest CAPTCHA is Text CAPTCHA where characters with some noise are presented to the user to type these characters where he could do that but the bot programs cannot. In spite of the fact that this system offers great security and limits of confinement programmed enrollment to web administrations, Text CAPTCHA has a few weaknesses which enable programmers to reach the mechanism of the CAPTCHA. This paper presents an improved Text CAPTCHA method based on the form of Letters.


INTRODUCTION
The internet contributes significantly to numerous parts of human life, for example, chatting, education, and online business activities and etc. Some web services have online registration where the users provide information in order to connect and use services such as email in Yahoo, Gmail, and Hotmail. However, many programs have been created by hackers which consequently entire website pages with inaccurate data which can cause activity clog, limit the execution of the framework and at times, even causing it to fail, especially where a site has countless. Therefore, researchers built up a system to recognize human clients and PC programs on account of online registration. The standard component utilized right now to address this issue is CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart). The idea of CAPTCHA depends on the capacity of people to do certain assignments which PC programs can't, for example, requesting that clients solve a distorted text or pick a specific picture from numerous showed pictures. In recent years, numerous kinds of CAPTCHAs have been created. Where are based on text, image, audio, video or based on the puzzle. The first and least difficult CAPTCHA is Text CAPTCHA where a alternation of letters and digits present to the user with adding a few changes to the characters, for example, noise, diffusing, rotating or making characters as 3D these adjustments added to keep bot programs from perusing the actual characters. Although this type presented good security it has been broken by new bot programs such as the mechanism of segmentation letters. This paper will suggest new CAPTCHA type based on the form of letters (Capital &small) and test this method by using PHP. In addition, measure their usability toward users. The rest of this paper will be organized as follows: Section II introduces Definition, Application, History, and categories of CAPTCHA. Section III presents the CAPTCHA based on the form of. Section V displays the results of CAPTCHA users and their analysis. Finally, Section VI summarizes the paper and presents the main conclusions.

A. Definition of CAPTCHA
"A CAPTCHA is a program that protects websites against bots by generating and grading tests that humans can pass but current computer programs cannot. For example, humans can read distorted text as the one shown below in figure (1) but current computers cannot" [1].

D. Classification of CAPTCHAs
The significance of CAPTCHA acquaints a test reaction test with the clients despite the fact that human or bot programs. The CAPTCHAs can be arranged into five sorts rely upon what is misshaped that is whether characters, digits, or pictures. These sorts are given beneath. [7], [1].

CAPTCHA Based on a text
Text-based is easy to execute where a succession of letters and digits present to the client with adding a few alterations to the characters, for example, noise, dispersion, rotating or making characters as 3D these changes added to keep bot programs from perusing the real characters [7], [1].A few cases are appeared underneath in the Figure  (2). Text-based CAPTCHA is the least difficult sort of CAPTCHA where it is the principal compose which has been concocted and actualized in Email administrations and web index. text-based CAPTCHA comprises of English letters and numbers. these characters are constrained so the bot projects and programmers can fathom the text CAPTCHA by outlining programs which filter the content CAPTCHA and writing it in the particular place. This issue is solved by doing some alteration on characters, for example, including some noise or rotate and scatter letters or present characters as corrupted and distorted letters or present characters as 3D. these alterations make a few issues for the client when he distinguishes the right characters since a few characters have comparable shapes in the wake of making modifications.in an expansion, Another issue in textbased CAPTCHA is introduced by English dialect where a few clients can't see a few kinds of text-based CAPTCHA, for example, clickable CAPTCHA and Strangeness in Sentences CAPTCHA. [1], [7], [8], [9][10].

CAPTCHA based on image
Image-based CAPTCHAs are situated in light of perceiving a particular picture from similarity pictures and now and then are blended with a few words. It is troublesome for Bot projects to recognize the designs where human clients can do that. Figure (3) indicates image CAPTCHA. [1], [7], [11], [12].

Figure (3) Image CAPTCHA
In spite of the fact that this type is simple, there are a few issues can confront the client when he is endeavoring to identify picture based CAPTCHA: 1) Some clients who have low vision or learning incapacity will meet a few issues when they are endeavoring to solve this CAPTCHA. 2) A probability of break the CAPTCHA by bot programs will increment if the quantity of decision is diminished so it is smarter to make more choices in the CAPTCHA to make it strong however this technique will exhaust the database. 3) This CAPTCHA is accessible just by the English language in this manner English speakers and some other people who have English vocabulary learning will comprehend the CAPTCHA only. [1], [11], [12].

CAPTCHA based on audio
CAPTCHA based sound speak depicted in presenting acquainting words to the client as a form of voice, so the client is asked to type what he/she has listened to solve the CAPTCHA. The characteristics of this sort are that it can be utilized for visually impaired users. Figure (4) represents audio CAPTCHA.

CAPTCHA based on puzzle
In puzzle CAPTCHAs, the client is required solve a conundrum which depicts on presenting lumps of a picture and requesting that client to consolidate the pieces or recognize a particular piece of the picture. A portion of the techniques in this class are given as below in the Figure ( [7].

III. PROPOSED METHOD
In our CAPTCHA, the user is required to type the characters (capital or small) exactly as it is required. The steps involved in using this CAPTCHA are explained as follows: Step 1: A random sequence of letters is shown to the user. It is not important for these letters to have to mean, as this will strengthen this type of CAPTCHA from being compromised. These letters may contain a mix of both capital and small letters.
Step 2: A random set of instructions is shown to the user. These instructions inform the user as to the form of characters (capital or small) the user is required to enter. These instructions can also be conveyed by using the letter C to indicate a capital is required and the letter s to indicate a small letter is required.
Step 3: The user should enter the text as required. If the entered letters match the requirements, the user will be allowed to continue with the registration or will be given website access. Otherwise, different text with different instructions will be given to the user for a second attempt. Figure 7 shows CAPTCHA based on the form of letters.

Figure (7) CAPTCHA based on the form of letters
Noise and scattering can be added or the letters in the text can be rotated to make it more difficult for Bots and hackers, however, it is important that the level of difficulty does not cause confusion for the user in terms of entering capital or small letters.
CAPTCHA based on the form of letters has been implemented by using Php programming where the CAPTCHA was designed with showing the user an example of how to solve the CAPTCHA if he doesn't how to solve it as it is shown in Figure (

01
In our CAPTCHA when the user input wrong word the system will present another new CAPTCHA until he inputs the write one, in our design, we put a counter to count how many attempts for each user to solve the CAPTCHA. After the user has solved the CAPTCHA correctly the system will ask the user to input his/her name, age, gender, nationality and rate the CAPTCHA (complex or Very Hard or Hard or Easy or Very easy).to use this information for analyzing the results as shown in the Figure (9).

V. RESULTS AND DISCUSSION
The CAPTCHA based on the form of letters has been hosted in website http://it-del.uot.edu.ly/captcha and we asked many volunteers from different countries with different background and age to test this CAPTCHA. We take 100 results of volunteers and analysis the results. As it can be observed from Figure (9) the user has to fill four information which are age, gender, nationality and rates the CAPTCHA. We show different graphs, describing the responses of users. For instance, as it can be observed from Figure 10 that the participation of male and female is nearly equal where about 56% of the participants were male and about 41% were female.   Figure 13 shows the number of attempts a user had to take the test before providing a correct response. As it can see in Figure 13 the majority of people could resolve the CAPTCHA at first attempt. However, 14% of the users needed two attempts to respond to the challenge, and only 11% of the participants needed three or more attempts. Figure 14 presented the rate of users toward this CAPTCHA.  and sophisticated application can confuse the user and consequently, it will negatively affect the user's usability and performance levels.in CAPTCHA based in the form of letters, the results of testing interaction with the CAPTCHA was very good where it was nearly a half of users said that is easy and 38% very easy. However, 13% found that is hard and only 2 % stated that is very hard.

VI. CONCLUSIONS
CAPTCHA plays important role in World Wide Web security where it prevents Bot programs and Hackers from abusing online services. This paper has introduced concepts and history of CAPTCHAs, CAPTCHA applications and describing the classification of CAPTCHA methods based on text, images, voice, video, and puzzle. This paper has also presented new mechanism of text CAPTCHA called CAPTCHA based on the form of letters where the user has to write text with following the instruction, which letters have to wrote Capital and which letters have to wrote small. Finally, we tested the usability and performance levels of this CAPTCHA and we found that it is suitable and appropriate fashion for the human interaction.