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Detailed explanation of how PHP randomly generates image verification codes

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Release： 2016-07-25 08:52:44
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  2. session_start();
  3. //Randomly generate a string of verification codes
  4. function random($len) {
  5. $srcstr="ABCDEFGHIJKLMNPQRSTUVWXYZ123456789";
  6. mt_srand();
  7. $strs=" ";
  8. for($i=0;$i<$len;$i++) {
  9. $strs.=$srcstr[mt_rand(0,33)];
  10. }
  11. return ($strs);
  12. }
  13. $str =random(5); //Randomly generated string
  14. $width=60; //Width of the verification code image
  15. $height=25; //Height of the verification code image
  16. //Date in the past
  17. header(" Expires:Mon,26 Jul 1997 05:00:00 GMT");
  18. //always modified
  19. header("Last-Modified:".gmdate("D,d M Y H:i:s")."GMT");
  20. //HTTP/1.1
  21. header("Cache-Control:no-store,no-cache,must-revalidate");
  22. header("Cache-Control:post-check=0,pre-check=0",false );
  23. //HTTP/1.0
  24. header("Pragma:no-cache");
  25. header("Content-Type:image/png");
  27. $im=imagecreate($width,$height);
  28. $ back=imagecolorallocate($im,0xFF,0xFF,0xFF); //Background color
  29. $pix=imagecolorallocate($im,187,190,247); //Blurry point color
  30. $font=imagecolorallocate($im,41,163,238); //Font Color
  31. //Draw 1000 blurred points
  32. mt_srand();
  33. for($i=0;$i<1000;$i++) {
  34. imagesetpixel($im,mt_rand(0,$width),mt_rand(0 ,$height),$pix);
  35. }
  36. imagestring($im,5,7,5,$str,$font);//Draw a randomly generated string
  37. imagerectangle($im,0,0,$width -1,$height-1,$font);//Draw a 1px border around the verification code image
  38. imagepng($im);//Create a PNG format graphic
  39. imagedestroy($im);//Handle the image Deconstruct and release in memory space
  40. $_SESSION["auth_code"]=$str;
  41. ?>
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Example 2, PHP random verification code php generates simple verification code

  2. $image_width=140;
  3. $image_height=50;
  4. srand(microtime()*10000);
  5. for($i=0;$i<4;$i++){
  6. $number.=dechex(rand(0,15));
  7. }
  8. $check=$number;
  9. $im=imagecreate($image_width,$image_height);
  10. imagecolorallocate($im,255,255,255);
  11. for($i =0;$i $font=rand(40,80);
  12. $x=rand(1,8)+$image_width*$i/4;
  13. $y= rand(1,$image_height/4);
  14. $color=imagecolorallocate($im,rand(0,100),rand(0,150),rand(0,200));
  15. imagestring($im,$font,$x,$y, $check[$i],$color);
  16. }
  17. imagepng($im);
  18. imagedestroy($im);
  19. ?>
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Related labels：
php随机生成图片验证码方法详解
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