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PHP验证码实现原理

生成随机数或者字母保存到session中(验证验证码的时候用),然后对生成的数字或者字母进行绘图!然后呈现在我们眼前

刷新验证码:用js改变验证码图片所带的参数,让浏览器不读缓存的图片,从而实现刷新验证码效果!

代码示例

$str="QWERTYUIOPASDFGHJKLZXCVBNM1234567890";

$image=imagecreate(50,25);
imagecolorallocate($image,mt_rand(0,125),mt_rand(0,125),mt_rand(0,125));
$color = imagecolorallocate($image,mt_rand(200,255),mt_rand(200,255),mt_rand(200,255));
for($i=1;$i<=4;$i  ) {
$date=$str[mt_rand(0,strlen($str)-1)];
$code.=$date;
}
session_start();
$_SESSION['code'] = $code;
imagestring($image,4,8,4,$code,$color);
for($i=1;$i<=30;$i  ) {
imagesetpixel($image,mt_rand(0,50),mt_rand(0,25),mt_rand(125,200));
}
for($i=1;$i<=mt_rand(1,5);$i  ) { imageline($image,mt_rand(0,50),mt_rand(0,25),mt_rand(0,50),mt_rand(0,25),mt_rand(100,150)); } header("content-type:image/png"); imagepng($image); ?>
数字 字母验证码（各字母颜色不同）：

 $str="QWERTYUIOPASDFGHJKLZXCVBNM1234567890";
$image=imagecreate(50,25);
imagecolorallocate($image,mt_rand(0,125),mt_rand(0,125),mt_rand(0,125));
$color[0] = imagecolorallocate($image,mt_rand(200,255),mt_rand(200,255),mt_rand(200,255));
$color[1] = imagecolorallocate($image,mt_rand(200,255),mt_rand(200,255),mt_rand(200,255));
$color[2] = imagecolorallocate($image,mt_rand(200,255),mt_rand(200,255),mt_rand(200,255));
$color[3] = imagecolorallocate($image,mt_rand(200,255),mt_rand(200,255),mt_rand(200,255));
for($i=0;$i<4;$i  ) {
$date=$str[mt_rand(0,strlen($str)-1)];
$code.=$date;
imagestring($image,5,6 $i*10,4,$code[$i],$color[$i]);
}
session_start();
$_SESSION['code'] = $code;
for($i=1;$i<=30;$i  ) {
imagesetpixel($image,mt_rand(0,50),mt_rand(0,25),mt_rand(125,200));
}
for($i=1;$i<=mt_rand(1,5);$i  ) {
imageline($image,mt_rand(0,50),mt_rand(0,25),mt_rand(0,50),mt_rand(0,25),mt_rand(100,150));
}
header("content-type:image/png");
imagepng($image);

来自：php验证码实现原理

驗證碼, php