how to share images between wpf and asp.net?

An easy and strait forward way is to put all your images in a seperated Class (or in your case in MyCore) as a Ressource (Turn access modifier to public!).

At this point you can use an HTTPHandler as ImageHandler, which streams the images of your ressource file as "normal" images to your webpage, e.g.

public class ImageHandler : IHttpHandler
{
  public void ProcessRequest(HttpContext context)
  {
    context.Response.ContentType = "image/jpg";
    context.Response.Clear();

    Bitmap image = ClassLibrary1.Resource1._1346135638012;
    image.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);

  }

  public bool IsReusable
  {
    get
    {
        return false;
    }
   }
 }

You could use a get parameter to identify which images has to be streamed, e.g.

<image src="./ImageHandler.ashx?ImageId=123" />

And - of course - you could use the ressoures for your application as well.