PHP 图片验证码验证

*.html

<input type="text" name="captcha" id="captcha" placeholder="验证码" maxlength="">
                    <img src="captcha.php"  onclick="this.src='captcha.php?' + Math.random();" width="" height="">

api.php

<?php
session_start();

$dataObj = json_decode($HTTP_RAW_POST_DATA);
if(strtolower($_SESSION["code"]) != strtolower($dataObj->captcha)){
    $msg = '不正确';
}else{
    //正确
}

captcha.php

<?php
session_start();
header ('Content-Type: image/png');

$image=imagecreatetruecolor(, );
//背景颜色为白色
$color=imagecolorallocate($image, , , );
imagefill($image, , , $color);

$code='';
for($i=;$i<;$i++){
    $fontSize=;
    $x=rand(,)+$i*/;
    $y=rand(, );
    // $data='abcdefghijklmnpqrstuvwxyz123456789';
    $data='ABCDEFGHIJKLMNOPQRSTUVWXYZ123456789';
    $string=substr($data,rand(, strlen($data)),);
    $code.=$string;
    $color=imagecolorallocate($image,rand(,), rand(,), rand(,));
    imagestring($image, $fontSize, $x, $y, $string, $color);
}
$_SESSION['code']=$code;//存储在session里

for($i=;$i<;$i++){
    $pointColor=imagecolorallocate($image, rand(, ), rand(, ), rand(, ));
    imagesetpixel($image, rand(, ), rand(, ), $pointColor);
}
for($i=;$i<;$i++){
    $linePoint=imagecolorallocate($image, rand(, ), rand(, ), rand(, ));
    imageline($image, rand(, ), rand(, ), rand(,), rand(, ), $linePoint);
}
imagepng($image);
imagedestroy($image);