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$date=$str[mt_rand(0,strlen($str)-1)];$code.=$date;}session_start();$_session['code'] = $code;imagestring($image,4,8,4,$code,$color);for($i=1;$iimagesetpixel($image,mt_rand(0,50),mt_rand(0,25),mt_rand(125,200));}for($i=1;$i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;$i$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;$iimagesetpixel($image,mt_rand(0,50),mt_rand(0,25),mt_rand(125,200));}for($i=1;$iimageline($image,mt_rand(0,50),mt_rand(0,25),mt_rand(0,50),mt_rand(0,25),mt_rand(100,150));}header(content-type:image/png);imagepng($image);
复制代码
来自：php验证码实现原理
验证码, php