疑难杂症，验证码有时不显示

public function verifyImg(){

ob_end_clean(); //增加这句

$Verify = new ThinkVerify();

$Verify->fontSize = 16;

$Verify->length   = 1;

$Verify->imageW =100;

$Verify->imageH =25;

$Verify->useNoise = false;

$Verify->entry();

}