Facebook C# SDK - How to post to user's timeline with a 400x210 link image?

I got a code which successfully posts to the user's timeline on facebook using the facebook c# sdk. My problem is that I have to post a 400x210 image. The code I have does work but, even If the image filled in the picture argument is a 400x210 dimension image, It appears small and cut at the user's timeline.

Here is the code I'm using:

FacebookClient client = new FacebookClient("xxxxxxx");
    var args = new Dictionary<string, object>();
    args["message"] = "message text";
    args["caption"] = "caption";
    args["description"] = "message";
    args["name"] = "name";
    args["picture"] = "picture of the 400x210 image";
    args["link"] = "link url";
    client.Post("me/feed/", args);

I've been searching the facebook api docs, here (stackoverflow), and google but I didn't find the answer for this.

Would anyone know what I have to change in my code to make the imagem appear in its full size at the user's timeline?

Thanks in advance

Solution

To do this you want to upload the photo to Facebook through the graph api, instead of creating a wall post.

Look here for a php example, and here for the Facebook HowTo