Support for Chinese, Alphabet, and digital php captcha _php instances

In this paper, we demonstrate 5 kinds of verification codes, and describe the function of generating verification code. PHP generated Verification code principle: Through the GD library, generate a picture with a verification code, and save the Verification code in the session.

Session_Start ();   GetCode (4,60,20);   function GetCode ($num, $w, $h) {$code = "";   for ($i = 0; $i < $num; $i + +) {$code. = rand (0, 9);   }//4-bit verification code can also be generated directly with Rand (1000,9999)//The generated verification code is written to the SESSION, the verification with $_session["helloweba_num"] = $code;   Create a picture, define the color value header ("Content-type:image/png");   $im = Imagecreate ($w, $h);   $black = imagecolorallocate ($im, 0, 0, 0);   $gray = Imagecolorallocate ($im, 200, 200, 200);   $bgcolor = Imagecolorallocate ($im, 255, 255, 255);     Fill Background imagefill ($im, 0, 0, $gray);     Draw Border Imagerectangle ($im, 0, 0, $w-1, $h-1, $black);   Randomly draws two dashed lines, acts as a disturbance $style = Array ($black, $black, $black, $black, $black, $gray, $gray, $gray, $gray, $gray);   Imagesetstyle ($im, $style);   $y 1 = rand (0, $h);   $y 2 = rand (0, $h);   $y 3 = rand (0, $h);   $y 4 = rand (0, $h);   Imageline ($im, 0, $y 1, $w, $y 3, img_color_styled);     Imageline ($im, 0, $y 2, $w, $y 4, img_color_styled);   A large number of black dots are randomly generated on the canvas, which acts as interference; for ($i = 0; $i < $i + +) {Imagesetpixel ($im, rand (0,$W), rand (0, $h), $black);   The numbers are randomly displayed on the canvas, and the horizontal spacing and position of the characters are randomly generated according to a certain range of fluctuations $strx = rand (3, 8);     for ($i = 0; $i < $num; $i + +) {$strpos = rand (1, 6);     Imagestring ($im, 5, $strx, $strpos, substr ($code, $i, 1), $black);   $strx + = rand (8, 12); } imagepng ($im);//Output Picture Imagedestroy ($im);//release Image Memory}

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