文件名：原来为ValidationCode.php
修改为validate.php后可以正常显示验证码，
浏览器中请求code.php文件中进行显示验证码

<?php
    class ValidationCode{
        private $width;
        private $height;
        private $num_chars;
        private $image;
        const BORDER = 1;

        function __construct($width=60,$height=20,$num_chars=4){
            $this->width = $width;
            $this->height = $height;
            $this->num_chars = $num_chars;
        }
        
        function showImage(){
            $this->createImage();
            $this->drawBorder();
            $this->drawChars();
            $this->outPic();
        }
        
        //create canvas
         function createImage(){
            $this->image = imagecreate($this->width,$this->height);
            //$rand_color = imagecolorallocate($this->image,rand(0,255),rand(0,255),rand(0,255));
            $back = imagecolorallocate($this->image,0,0,0);
            $border = imagecolorallocate($this->image,255,255,255);
            imagefill($this->image,0,0,$back);
            //imagefilledrectangle($thid->image,self::BORDER,self::BORDER,$this->width-self::BORDER,$this->height-self::BORDER,$border);
            //imageline($this->image,1,1,100,100,$rand_color);
            //$this->outPic();
        }

        //draw border
        private function drawBorder(){
            $outer_bg_color = imagecolorallocate($this->image,0,0,0);
            $inner_bg_color = imagecolorallocate($this->image,255,255,255);
            imagefill($this->image,0,0,$outer_bg_color);
            imagefilledrectangle($this->image,self::BORDER,self::BORDER,$this->width-self::BORDER-1,$this->height-self::BORDER-1,$inner_bg_color);

        }        
    
        //create char content
          function createChar(){
            $rand_ascii="";
            $rand_type = rand(0,2);
            switch($rand_type){
                case 0:
                    $rand_ascii = rand(48,57);  
                   break;
                case 1:
                     $rand_ascii = rand(65,90);
                   break;
                case 2:
                     $rand_ascii = rand(97,122);
                   break;
            }
            $rand_str = sprintf("%c",$rand_ascii);
            return $rand_str;
        }
    
    
    
        //draw char
         private function drawChars(){
            $x = $this->width/$this->num_chars+1;
            $y = $this->height/2;
            for($index = 0; $index<$this->num_chars; $index++){
                $rand_color = imagecolorallocate($this->image,rand(0,255),rand(0,255),rand(0,255));
                imagechar($this->image,3,$x*$index+2,$y-$y/2,$this->createChar(),$rand_color);
            }
        }

        //out pic
        private function outPic(){
            header("content-type:image/png");
            imagepng($this->image);
        }
        

         function __destruct(){
             imagedestroy($this->image);
         }
    }
    
    /*$code = new ValidationCode();
    //echo $code->createChar();
    $code->showImage();*/
?>

code.php

<?php
     require_once("validate.php");
    $code = new ValidationCode();
    //echo $code->createChar();
    $code->showImage();
  ?>