Laravel 4 mews验证没有错误，但没有显示图片

I have a problem with mews captcha package. I have an application on Laravel 4.2. In this application there is a feedback form. I am using mews captcha package in it. But captcha picture not showing. I have enabled gd library. this is my config/app.php:

providers

'Mews\Captcha\CaptchaServiceProvider'

alias:

'Captcha'         => 'Mews\Captcha\Facades\Captcha',

and html where I am calling captcha:

<span class="input-group-addon">{{ HTML::image(Captcha::img()) }}</span>

Can you help me?

EDIT

html in brouser:

And this is, if I open captcha url in brouser:

EDIT2

code inspector:

EDIT3:

when I tried to save it in jpeg or jpg format, and opened it