Save BitmapImage to File

When you create your BitmapImage from a Uri, time is required to download the image.

If you check the following property, the value will likely be TRUE

objImage.IsDownloading

As such, you much attach a listener to the DownloadCompleted event handler and move all processing to that EventHandler.

objImage.DownloadCompleted += objImage_DownloadCompleted;

Where that handler will look something like:

private void objImage_DownloadCompleted(object sender, EventArgs e)
{
  JpegBitmapEncoder encoder = new JpegBitmapEncoder();
  Guid photoID = System.Guid.NewGuid();
  String photolocation = photoID.ToString() + ".jpg";  //file name 

  encoder.Frames.Add(BitmapFrame.Create((BitmapImage)sender));

  using (var filestream = new FileStream(photolocation, FileMode.Create))
    encoder.Save(filestream);
} 

You will likely also want to add another EventHandler for DownloadFailed in order to gracefully handle any error cases.

Edit

Added full sample class based on Ben’s comment:

public partial class MainWindow : Window
{
  public MainWindow()
  {
    InitializeComponent();

    SavePhoto("http://www.google.ca/intl/en_com/images/srpr/logo1w.png");
  }

  public void SavePhoto(string istrImagePath)
  {
    BitmapImage objImage = new BitmapImage(new Uri(istrImagePath, UriKind.RelativeOrAbsolute));

    objImage.DownloadCompleted += objImage_DownloadCompleted;
  }

  private void objImage_DownloadCompleted(object sender, EventArgs e)
  {
    JpegBitmapEncoder encoder = new JpegBitmapEncoder();
    Guid photoID = System.Guid.NewGuid();
    String photolocation = photoID.ToString() + ".jpg";  //file name 

    encoder.Frames.Add(BitmapFrame.Create((BitmapImage)sender));

    using (var filestream = new FileStream(photolocation, FileMode.Create))
      encoder.Save(filestream);
  } 
}