You can send these parameters with your request:
image required A binary file, base64 data, or a URL for an image
album optional The id of the album you want to add the image to. For anonymous albums, {album} should be the deletehash that is returned at creation.
type optional The type of the file that's being sent; file, base64 or URL
name optional The name of the file, this is automatically detected if uploading a file with a POST and multipart / form-data
title optional The title of the image.
description optional The description of the image.
So, how about this:
curl_setopt($ch, CURLOPT_POSTFIELDS, array('image' => base64_encode($image), 'album' => 1234));