there are multiple ways to use curl to upload image files, e.g.:
$ch = curl_init();
$data = array('name' => 'Foo', 'file' => '@/path/to/image.jpeg');
curl_setopt($ch, CURLOPT_URL, 'http://localhost/upload.php');
curl_setopt($ch, CURLOPT_POST, 1);
//CURLOPT_SAFE_UPLOAD defaulted to true in 5.6.0
//So next line is required as of php >= 5.6.0
curl_setopt($ch, CURLOPT_SAFE_UPLOAD, false);
curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
curl_exec($ch);
you can check the examples at: http://au.php.net/manual/en/function.curl-setopt.php