<?phpsession_start();srand((double)microtime()*1000000); while(($authnum=rand()%10000)<1000);//生成四位随机整数验证码 $_SESSION['auth']=$authnum;//生成验证码图片 Header("Content-type: image/PNG");$im = imagecreate(55,18); $red = ImageColorAllocate($im, 255,0,0); $white = ImageColorAllocate($im, 200,200,100); $gray = ImageColorAllocate($im, 250,250,250); $black = ImageColorAllocate($im, 120,120,50); imagefill($im,60,20,$gray); //将四位整数验证码绘入图片 //位置交错for ($i = 0; $i < strlen($authnum); $i++){    $i%2 == 0?$top = -1:$top = 3;    imagestring($im, 6, 13*$i+4, 1, substr($authnum,$i,1), $white); }for($i=0;$i<100;$i++)   //加入干扰象素 {     imagesetpixel($im, rand()%70 , rand()%30 , $black); } ImagePNG($im); ImageDestroy($im);?>