Hello 
 I know the ticket was open a while ago but i have been looking for this complete code for a while and I only found pieces of it on the net but nothing that fully worked, so here it is. I hope it helps some people.
I saw your post and i had exactly the same issue using most of the information found here - main author of the code below with w3schools.
Here is how it can be done, two ways : 
1- your upload form or function is on the server that receives the file
// the index.php file on the server
<br><br>
<?php /* includes */ require_once 'upload.php'; ?>
<!DOCTYPE html>
<html><body> Formulaire de téléchargement d'une image <br><br>
<form action="upload.php" method="POST" enctype="multipart/form-data">
    Select image to upload:
    <input type="file" name="fileToUpload" id="fileToUpload">
    <input type="submit" value="Upload Image" name="submit">
</form>
</body> </html>
 the upload.php file, in the same dir in this case
<?php
// writing in a sublfolder called image 
$target_dir = "image/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
$uploadOk = 1;
$imageFileType = pathinfo($target_file,PATHINFO_EXTENSION);
// Check if image file is a actual image or fake image
if(isset($_POST["submit"])) {
    $check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
    if($check !== false) {
        echo "File is an image - " . $check["mime"] . ".";
        $uploadOk = 1;
    } else {
        echo "File is not an image.";
        $uploadOk = 0;
    }
}
if ($uploadOk == 0) {
    echo "Sorry, your file was not uploaded.";
// if everything is ok, try to upload file
} else {
    // give a name and direction to the image - i changed the name to test.jpg...
    $uploadfile = $_SERVER['DOCUMENT_ROOT'].$target_dir.'test.jpg';
    echo "<br><br>";
    echo $uploadfile;
         echo "<br><br>";
    if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $uploadfile)) {
        echo "The file ". basename( $_FILES["fileToUpload"]["name"]). " has been uploaded.";
    } else {
        echo "Sorry, there was an error uploading your file.";
    }
}
?>
2- Second option, if your webserver is different from the server receiving the file, here you will need to have two files one on each server :
Server that sends the file (your web server) : send.php
<?php
    // I uploaded a file called sample2.jpeg from on server to another
    // again you can make functions out of this
    $target_url = 'http://192.168.56.103/receive.php';
        //This needs to be the full path to the file you want to send.
$file_name_with_full_path = realpath('./sample2.jpeg');
            /* curl will accept an array here too.
             * Many examples I found showed a url-encoded string instead.
             * Take note that the 'key' in the array will be the key that shows up in the
             * $_FILES array of the accept script
             */
        //$post = array('extra_info' => '123456','file_contents'=>'@'.$file_name_with_full_path);
        $post = array('file_contents' => new CurlFile($file_name_with_full_path, 'text/plain' /* MIME-Type */,'' /*directory*/));
            $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL,$target_url);
        curl_setopt($ch, CURLOPT_POST,1);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
        $result=curl_exec ($ch);
        curl_close ($ch);
        echo $result;
    ?>
 and the file on the receiving server end : receive.php
<?php
// you can chage the destination path
$uploaddir = realpath('./') . '/';
$uploadfile = $uploaddir . basename($_FILES['file_contents']['name']);
echo "<br><br>";
print_r ($uploadfile);
echo "<br><br>";
echo '<pre>';
        if (move_uploaded_file($_FILES['file_contents']['tmp_name'], $uploadfile)) {
            echo "File is valid, and was successfully uploaded.\n";
        } else {
            echo "Possible file upload attack!\n";
        }
        echo 'Here is some more debugging info:';
        print_r($_FILES);
        echo "\n<hr />\n";
        print_r($_POST);
print "</pr" . "e>\n";
?>
<br><br>Sources and references to other codes : 
<br>http://stackoverflow.com/questions/12667797/using-curl-to-upload-post-data-with-files
<br>http://stackoverflow.com/questions/15200632/how-to-upload-file-using-curl-with-php
<br>http://code.stephenmorley.org/php/sending-files-using-curl/
<br>http://www.w3schools.com/php/php_file_upload.asp
Thanks again to the true authors of 99% of the code, fixed with peoples comment on stackoverflow forum : derakkilgo and W3SCHOOLS.