how to save an image to a specific directory

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C#

WPF

I have a WPF application where there is an image control and when I click on it, an OpenFileDialog displays in order to choose an image from a file! now I want to save this image to a specific folder called working_folder

this is the location of the folder I want to save the image to:

System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetEntryAssembly().Location) + "\\working_folder\\";

and the location of the image is this D:\Users\mowglin\Pictures\Images, and the image is type ".tif"
Please see the code below to make this more clear:

bool imgLoaded = false;

            Image currentImg = (Image)sender;
            if (currentImg.Tag != null)
            imgLoaded = (bool)currentImg.Tag;
            if (!imgLoaded)
            {
                string filename = "";
                OpenFileDialog dlg = new OpenFileDialog();
                dlg.DefaultExt = ".tif";
                dlg.Filter = "(*.tif,*.tiff)|*.tif;*.tiff";
                bool result = (bool)dlg.ShowDialog(this);
                if (result == true)
                {
                    filename = dlg.FileName;
                    currentImg.Source = new BitmapImage(new Uri(filename));
                    this.UpdateLayout();
                    currentImg.Tag = true;
                }
            }

so my question is, how can I save the image to a specefic directory?