<?php
session_start(); //设置session,一定要在顶部
$width = 150; //设置图片宽为300像素
$height = 40; //设置图片高为40像素
$image = imagecreatetruecolor($width, $height); //设置验证码大小的函数
$bgcolor = imagecolorallocate($image, 255, 255, 255); //验证码颜色RGB为(255,255,255)#ffffff
imagefill($image, 0, 0, $bgcolor); //区域填充
$cap_code = "";
for($i=0;$i<4;$i++){
    $fontsize = 7; //设置字体大小
    $fontcolor = imagecolorallocate($image, rand(0,120), rand(0,120), rand(0,120));
    //数字越大，颜色越浅，这里是深颜色0-120
    $fontcontent = rand(0,9);
    $cap_code.=$fontcontent; //.=连续定义变量
    $x = ($i*150/4)+rand(5,10);
    $y = rand(5,10);
    //设置坐标
    imagestring($image, $fontsize, $x, $y, $fontcontent, $fontcolor);
}
$_SESSION['code'] = $cap_code; //存到session
//设置干扰元素，设置雪花点
for($i=0;$i<300;$i++){
    $inputcolor = imagecolorallocate($image, rand(50,200), rand(20,200), rand(50,200));
    //设置颜色，20-200颜色比数字浅，不干扰阅读
    imagesetpixel($image, rand(1,149), rand(1,39), $inputcolor);
    //画一个单一像素的元素
}
//增加干扰元素，设置横线(先设置线的颜色，在设置横线)
for ($i=0;$i<4;$i++) {
    $linecolor = imagecolorallocate($image, rand(20,220), rand(20,220),rand(20,220));
    //设置线的颜色
    imageline($image, rand(1,149), rand(1,39), rand(1,299), rand(1,149), $linecolor);
 
}
 
//因为有些浏览器，访问的content-type会是文本型（乱码），所以我们需要设置成图片的格式类型
header('Content-Type:image/png');
imagepng($image); //建立png函数
imagedestroy($image); //结束图形函数，消除$image

<?php
$iC = new idCode(5,60,30);
$iC->createPNG();

class idCode{
  private $words = array('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',
  '0','1','2','3','4','5','6','7','8','9');
  private $fonts;
  private $count;//验证码字符数
  private $height;
  private $width;
  private $path = '..\myfolder\fonts';
  private $keys;

  //构造函数
  public function __construct($count,$width,$height){
    $this->count = $count;
    $this->getFonts();
    $this->height = $height;
    $this->width = $width;
  }

  private function getFonts(){
    $dir = dir($this->path);

    while(false !== ($file = $dir->read())){
        if($file != '.' && $file != '..'){
          $this->fonts[count($this->fonts)] = basename($file);
        }
    }
    $dir->close();
  }

  private function createKeys(){
    for($i = 0;$i < $this->count;$i++){
      $this->keys[$i]['char'] = $this->words[rand(0,count($this->words)-1)];
      //使用字体路径标识
      $this->keys[$i]['filename'] = $this->path.'\\'.$this->fonts[rand(0,count($this->fonts)-1)];
    }
  }

  public function createPNG(){
    $this->createKeys();

    //创建画布以及颜色块儿
    $bg = imagecreatetruecolor($this->width + 10*2,$this->height + 3*2);//两边留10px空白,上下3px
    $grey = imagecolorallocate($bg,155,155,155);
    $blue = imagecolorallocate($bg,0x00,0x00,0xff);
    //填充背景
    imagefill($bg,0,0,$grey);
    //添加字符
    $pwidth = $this->width/$this->count;
    $x;$y;
    for($i = 0;$i < $this->count;$i++){
      $rotation = rand(-40,40);//偏转角度±40°
      $fontsize = 33;
      $width_txt;
      $height_txt;

      do{
        $fontsize--;
        $bbox = imagettfbbox($fontsize,$rotation,$this->keys[$i]['filename'],$this->keys[$i]['char']);
        $width_txt = $bbox[2] - $bbox[0];//x 0 2 4 6,y1 3 5 7;左下，右下，右上，左上
        $height_txt = $bbox[7] - $bbox[1];
      }while($fontsize > 8 && ($height_txt > $this->height || $width_txt > $pwidth));

      $fontcolor = imagecolorallocate($bg,rand(0,255),rand(0,255),rand(0,255));
      $x = 8 + $pwidth*$i + $pwidth/2 - $width_txt/2;//x坐标基本位置
      $y = $this->height/2 - $height_txt/2;

      imagettftext($bg,$fontsize,$rotation,$x,$y,$fontcolor,$this->keys[$i]['filename'],$this->keys[$i]['char']);
    }
    //绘制干扰线
    //根据字体酌情增加干扰线
    imageline($bg,0,15,40,10,$blue);
    //图像输出头文件
    header('Content-type:image/png');
    //输出png图像
    imagepng($bg);
    //清除缓存资源
    imagedestroy($bg);
  }

  public function checkKeys($input){
    if(count($input)!=$this->count){
      return 'ERROR:长度不正确.';
    }else{
      for($i=0;$i < $this->count;$i++){
        //0 o O I l 1 校准,根据所选择的字体确定是否需要手动校准
        if($input[$i] != $this->keys[$i]['char']){
          return 'SUCCESS.';
        }else{
          return 'ERROR:请输入正确验证码.';
        }
      }
    }
  }
}
?>