Ensure WPF Taskbar Window Preview is actualized

I believe you'd need to customize the preview, as described here (under the Customizing Preview section). Which leverages the Windows API Code Pack for Microsoft® .NET Framework.

An example can be found here, but looks like:

TabbedThumbnail preview = new TabbedThumbnail(parentForm.Handle, childForm.Handle);TaskbarManager.Instance.TabbedThumbnail.AddThumbnailPreview(preview);preview.TabbedThumbnailBitmapRequested += (o, e) =>    {        Bitmap bmp = new Bitmap(width, height);        // draw custom bitmap...        e.SetImage(bmp);        e.Handled = true;    };

Another example, can be found here which states:

The CustomWindowsManager class provides an abstraction of a customized window thumbnail preview and live preview (peek), including the facilities to receive a notification when a preview bitmap is requested by the Desktop Window Manager (DWM) and to automatically grab the preview bitmap of a window.

The download link for this code is here, which includes the CustomWindowsManager class. This appears to provide the live preview.

You probably can't. Windows 7 pipes the graphics of an open window to the live preview from the Taskbar. It can't know what the window now looks like while it is minimized because it isn't being drawn at all.

I guess it's not impossible to do custom thumbnails. Aside from CodeNaked's answer, I also found this article, which even includes multiple thumbnails from the same app.