.NET Download Captcha image and upload to upload form?

So i trying to download the captcha image from this website canhasbitcoin.com
i don't want to grab it and display it in the picturebox
i just want to download it to my computer.
After it downloads how would i upload it to this website manymacros.com/ss.php.
I try using httpwebrequest but it didn't work.
I know how to copy the picture and display it on the picturebox so far.
The html code for the upload form is.

Code 
<form action='ss.php' method='post' ENCTYPE="multipart/form-data">

KEY:

<input type="text" name="key" value=""/><br/>

UPLOAD THE FILE: 

<input type="hidden" name="cmd" value="upload"/>

<input type='file' name='file'/>

<br/>

<input type='submit' value='submit'/>

</form>