How PHP implements the verification code

Now, let's talk about simple, pure digital verification codes.

For beginners, it is recommended to follow the comments//numbers of my code. The simplest way to do this is to copy the entire code away.

Create a new captcha.php:

<?php//11> Set session, must be at the top of the script session_start ();    /* $image = Imagecreatetruecolor (100, 30);  1> set captcha picture size function//5> set CAPTCHA color imagecolorallocate (int im, int red, int green, int blue); $bgcolor = Imagecolorallocate ($image, 255,255,255); #ffffff the area of the//6> area filled with int imagefill (int im, int x, int y, int col) (x/y) is shaded, col represents the color to be painted Imagefill ($image, 0, 0, $b  Gcolor);        10> Set Variable $captcha _code = ""; *///7> Generate random numbers for ($i =0; $i <4; $i + +) {//set font size $fontsize = 6;      Set the font color, random color $fontcolor = imagecolorallocate ($image, Rand (0,120), Rand (0,120), Rand (0,120));    0-120 Dark Color//Set Number $fontcontent = rand (0,9);      10>.= continuously defines the variable $captcha _code. = $fontcontent;    Set coordinates $x = ($i *100/4) +rand (5,10);     $y = rand (5,10);  Imagestring ($image, $fontsize, $x, $y, $fontcontent, $fontcolor);  }//10> save to SESSION $_session[' authcode ' = $captcha _code; 8> add interference element, set Snowflake point for ($i =0; $i <200; $i + +) {//Set point color, 50-200 color is lighter than digital, do not disturb reading $pointcolor = ImagecoLorallocate ($image, Rand (50,200), Rand (50,200), Rand (50,200));  Imagesetpixel-draws a single pixel Imagesetpixel ($image, Rand (1,99), Rand (1,29), $pointcolor); }//9> Add interference element, set horizontal for ($i =0; $i <4; $i + +) {//set line Color $linecolor = Imagecolorallocate ($image, Rand (80,220), rand (80    , (+), rand (80,220));  Set line, 2.1-wire imageline ($image, Rand (1,99), Rand (1,29), Rand (1,99), Rand (1,29), $linecolor);  }//2> set head, image/png header (' content-type:image/png ');  3>imagepng () establishes the PNG graph function imagepng ($image); 4>imagedestroy () End graph function Destroy $image Imagedestroy ($image);

Then there is the code for the static page: index.html

<! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 transitional//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">
From index.html you can see that the submitted form is to form.php, so there is a form.php code to judge:
<?php  Header ("Content-type:text/html;charset=utf-8");      Set Header information  //isset () detects if the variable is set  if (Isset ($_request[' Authcode '))) {    session_start ();    Strtolower () lowercase function    if (strtolower ($_request[' authcode ") = = $_session[' Authcode ']) {      //jump page      echo" < Script language=\ "javascript\" > ";      echo "document.location=\"./form.php\ "";      echo "</script>";    } else{      //Tips and jump page      echo "<script language=\" javascript\ ">";      echo "Alert (' Input error! ');";      echo "document.location=\"./form.php\ "";      echo "</script>";    }    Exit ();  }
The display page is as follows:
Digital plus English Verification code, just change the captcha.php page 7 ", the other two pages do not need to move, the code is as follows:
<?php//11> Set session, must be at the top of the script session_start ();    $image = Imagecreatetruecolor (100, 30);  1> set captcha picture size function//5> set CAPTCHA color imagecolorallocate (int im, int red, int green, int blue); $bgcolor = Imagecolorallocate ($image, 255,255,255); #ffffff the area of the//6> area filled with int imagefill (int im, int x, int y, int col) (x/y) is shaded, col represents the color to be painted Imagefill ($image, 0, 0, $b  Gcolor);        10> Set Variable $captcha _code = "";//7> generate random letters and numbers for ($i =0; $i <4; $i + +) {//set font size $fontsize = 8;      Set the font color, random color $fontcolor = imagecolorallocate ($image, Rand (0,120), Rand (0,120), Rand (0,120));    0-120 Dark Color//Set the values that need to be randomly taken, removing the error-prone values such as 0 and o $data = ' abcdefghigkmnpqrstuvwxy3456789 ';    Take out the value, String intercept method strlen Gets the string length $fontcontent = substr ($data, Rand (0,strlen ($DATA)), 1);        10>.= continuously defines the variable $captcha _code. = $fontcontent;    Set coordinates $x = ($i *100/4) +rand (5,10);    $y = rand (5,10);  Imagestring ($image, $fontsize, $x, $y, $fontcontent, $fontcolor); }//10> save to SESSION $_session[' authcode ' = $captCha_code; 8> add interference element, set Snowflake point for ($i =0; $i <200; $i + +) {//Set point color, 50-200 color is lighter than digital, do not disturb reading $pointcolor = Imagecolorallocate ($image, R        and (50,200), Rand (50,200), Rand (50,200));  Imagesetpixel-draws a single pixel Imagesetpixel ($image, Rand (1,99), Rand (1,29), $pointcolor); }//9> Add interference element, set horizontal for ($i =0; $i <4; $i + +) {//set line Color $linecolor = Imagecolorallocate ($image, Rand (80,220), rand (80    , (+), rand (80,220));  Set line, 2.1-wire imageline ($image, Rand (1,99), Rand (1,29), Rand (1,99), Rand (1,29), $linecolor);  }//2> set head, image/png header (' content-type:image/png ');  3>imagepng () establishes the PNG graph function imagepng ($image); 4>imagedestroy () End graph function Destroy $image Imagedestroy ($image);
　　
How PHP implements the verification code