PHP生成图片验证码功能示例

<?php
/**
 * created by jetbrains phpstorm.
 * user: lee
 * to change this template use file | settings | file templates.
 */
header("content-type:image/png");
$validatelength=4;
$strtodraw="";
$chars=[
  "0","1","2","3","4",
  "5","6","7","8","9",
  "a","b","c","d","e","f","g",
  "h","i","j","k","l","m","n",
  "o","p","q","r","s","t",
  "u","v","w","x","y","z",
  "a","b","c","d","e","f","g",
  "h","i","j","k","l","m","n",
  "o","p","q","r","s","t",
  "u","v","w","x","y","z"
];
$imgw=80;
$imgh=25;
$imgres=imagecreate($imgw,$imgh);
$imgcolor=imagecolorallocate($imgres,255,255,100);
$color=imagecolorallocate($imgres,0,0,0);
for($i=0;$i<$validatelength;$i++){
  $rand=rand(1,58);
  $strtodraw=$strtodraw." ".$chars[$rand];
}
imagestring($imgres,5,0,5,$strtodraw,$color);
for($i=0;$i<100;$i++){
  imagesetpixel($imgres,rand(0,$imgw),rand(0,$imgh),$color);
}
imagepng($imgres);
imagedestroy($imgres);