php实现简单验证码

1.得到验证码字符串

/** 得到验证吗字符串
 * @param int $type
 * @param int $length
 * @return string
 */
function getVerifycode($type = 1,$length = 4){
/*
 * 根据$type的值生成不同类型的验证码
 * 根据$length的值生成不同长度的验证码
 *
 * $type == 1   纯数字
 * $type == 2   纯字母
 * $type == 3   字母数字混合
 * */
    if($type == 1){
        $chars = join("",range(0,9));
    }elseif($type == 2){
        $chars = join("",array_merge(range("a","z"),range("A","Z")));
    }elseif($type == 3){
        $chars = join("",array_merge(range("A","Z"),range("a","z"),range(0,9)));
    }else{
        exit("验证码类型输入错误!");
    }
    if($length>strlen($chars)){
        exit("验证码长度不够!");
    }
    $chars = str_shuffle($chars);
    return substr($chars,0,$length);
}

2.生成验证码图片

/** 生成验证码图片
 * @param int $width
 * @param int $height
 */
function getVerifyimage($width = 80,$height = 30){
    session_start();
/*
 * 根据$width和$height来生成验证码图片
 * */

//  创建画布
    $image=imagecreatetruecolor($width,$height);
    $white=imagecolorallocate($image,255,255,255);
    $black=imagecolorallocate($image,0,0,0);
//  用填充矩形来填充画布
    $type=1;
    $length=4;
    imagefilledrectangle($image,1,1,$width-2,$height-2,$white);
    $chars=getVerifycode($type,$length);
    $session_name="verifycode";
    $_SESSION[$session_name]=$chars;
//  将验证码写到图片
    for($i=0;$i<$length;$i++){
        $size=mt_rand(14,18);
        $x=5+$i*$size;
        $y=mt_rand(2,15);
        $color=imagecolorallocate($image,mt_rand(50,90),mt_rand(80,200),mt_rand(40,120));
        $text=substr($chars,$i,1);
        imagestring($image,$size,$x,$y,$text,$color);
    }
//    设置干扰元素
    for($i=0;$i<66;$i++){
        imagesetpixel($image,mt_rand(0,$width-1),mt_rand(0,$height-1),$color);
    }
    for($i=0;$i<6;$i++){
        imageline($image,mt_rand(0,$width-1),mt_rand(0,$width-1),mt_rand(0,$height-1),mt_rand(0,$height-1),$color);
    }
    header("content-type:image/gif");
    imagegif($image);
    imagedestroy($image);
}