Simple verification code identification code made by php, php verification code code_PHP tutorial

Simple verification code identification code made by php, php verification code code

I have always wanted to write this, but after a long time, I became interested and simply recorded it.

Verification Code

Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA), commonly known as verification code, is a fully automated public Turing test to tell Computers and Humans Apart. program. In a CAPTCHA test, the computer as the server automatically generates a question for the user to answer. This question can be generated and judged by a computer, but only a human can answer it. Since computers cannot answer CAPTCHA questions, the user who answers the questions can be considered a human.
Encyclopedia introduction

To put it simply, randomly generated characters are output on a picture [other forms of drag and drop/SMS verification codes, etc. are not considered here].

Common types

Thoughts

This article is for demonstration purposes only, so the verification code in the first picture is taken as an example.

Every point on the picture has its RGB value, which can be obtained through the color picker. From the naked eye, it can be seen that the verification code of the picture is a pure digital solid color background

It can be seen from the color picker that the background color RGB value of the verification code is (212,214,204)

Achievement

Let’s use PHP’s imagecolorsforindex function to obtain the RGB values ​​of all points in the image:

$url = 'http://210.32.33.91:8080/reader/captcha.php';
$im = imagecreatefromgif($url);
imagegif($im, '1.gif');
$rgbArray = array();
$res = $im;
$size = getimagesize($url);

$wid = $size['0'];
$hid = $size['1'];
for ($i = 0; $i < $hid; ++ $i) {
 for ($j = 0; $j < $wid; ++ $j) {
  $rgb = imagecolorat($res, $j, $i);
  $rgbArray[$i][$j] = imagecolorsforindex($res, $rgb);
 }
}

The results are as follows:

You may want to ask what is the use of this? Let's change the way to display the data, output □ for the background color, and output ■ for the verification code area, let's take a look again:

for ($i = 0; $i < $hid; $i ++) {
 for ($j = 0; $j < $wid; $j ++) {
  
  if ($rgbArray[$i][$j]['red'] == 212) {
   echo '□';
  } else {
   echo '■';
  }
 }
 echo "<br>";
}

Effect:

Isn’t it very clear now?

But you may still have questions. Although you can see it, how do you know how much it is?

Let’s analyze it below:

Each verification code is directly spaced by 4 spaces, left and right by 6/10 spaces, and top and bottom by 16/10 spaces.

Let’s remove these interference points to see more clearly:

Is it very clear? Some people may still ask, how can you know what the numbers on the picture are after you talk so much?

Okay, let me tell you my idea. We will replace the □ and ■ just now with 0 and 1, and the shape of these numbers is fixed, so that we can get every word of 0-9. Area 8*10 is composed of 0 and 1,

Let’s do every 8 segments again, remove the 4-space spacing, and loop through to get the 01 combination value of 0-9:

$dic = array(
 '00011000001111000110011011000011110000111100001111000011011001100011110000011000' => 0,
 '00011000001110000111100000011000000110000001100000011000000110000001100001111110' => 1,
 '00111100011001101100001100000011000001100000110000011000001100000110000011111111' => 2,
 '01111100110001100000001100000110000111000000011000000011000000111100011001111100' => 3,
 '00000110000011100001111000110110011001101100011011111111000001100000011000000110' => 4,
 '11111110110000001100000011011100111001100000001100000011110000110110011000111100' => 5,
 '00111100011001101100001011000000110111001110011011000011110000110110011000111100' => 6,
 '11111111000000110000001100000110000011000001100000110000011000001100000011000000' => 7,
 '00111100011001101100001101100110001111000110011011000011110000110110011000111100' => 8,
 '00111100011001101100001111000011011001110011101100000011010000110110011000111100' => 9
);

After obtaining these 10, they are combined into an array. Each time the RGB of the image is parsed and replaced with the corresponding array value, the verification code value is obtained. Let’s demonstrate below:

Finally, for the sake of accuracy, let’s take a look at 100 loops:

Haha, the accuracy is 100%

Write it at the end

The purpose of this article is to allow WEB developers to pay attention to safety when generating verification codes and please do not use them for illegal purposes.

The code is on github:

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