当我尝试从WPF中的RichTextBox手动删除图像时出现InvalidOperationException

I am trying to create an app where I can enter text and images into a RichTextBox, serialize it, then deserialize it and load it back to a RichTextBox so that I can change it later. When I load the images from the serialized xml file, everything displays correctly, but when I try to delete the image from the RichTextBox manually by pressing backspace, I get the following exception: Cannot serialize a non-public type 'System.Windows.Media.Imaging.BitmapFrameDecode'.I am trying to create an app where I can enter