C# - Creating A Jpeg From Several Overlapping Png's?

So on my site, a user has the ability to create an avatar. It's created by the user selecting from several images; there is a base "skin" image, and png's that overlap that image that depict hair, eyes, mouth, etc.

I cannot save the user's avatar to the project's files, so the user's avatar data is stored in the database, and the png's are overlapped on the fly and displayed to the user.

However, I'd like to have the ability for the user to download their avatar as a jpeg by going to a page.

I have this little example set up that is working correctly:

protected void Page_Load(object sender, EventArgs e)
{
//User has skin1.png, eyes3.png, and mouth8.png
Bitmap bit = new Bitmap(System.Drawing.Image.FromFile(Server.MapPath("/images/skin1.png")), 80, 106);
Response.ContentType = "image/jpeg";
bit.Save(Response.OutputStream, ImageFormat.Jpeg);
}

But, as you can see, I only have this working for a single image. I'd like to create a bitmap from the multiple png's and output a jpeg.