生成图片，为什么显示的这样？

Notice: Undefined variable: image in G:\xampp\htdocs\project\captcha.php on line 3

Notice: Undefined variable: image in G:\xampp\htdocs\project\captcha.php on line 4

Warning: imagecolorallocate() expects parameter 1 to be resource, null given in G:\xampp\htdocs\project\captcha.php on line 4

Notice: Undefined variable: image in G:\xampp\htdocs\project\captcha.php on line 5

Warning: imagefill() expects parameter 1 to be resource, null given in G:\xampp\htdocs\project\captcha.php on line 5

Notice: Undefined variable: image in G:\xampp\htdocs\project\captcha.php on line 8

Warning: imagepng() expects parameter 1 to be resource, null given in G:\xampp\htdocs\project\captcha.php on line 8

Notice: Undefined variable: image in G:\xampp\htdocs\project\captcha.php on line 10

Warning: imagedestroy() expects parameter 1 to be resource, null given in G:\xampp\htdocs\project\captcha.php on line 10