I was surprised how easy it is to enable your application to allow dragging things (eg. text or images) from the application to the desktop.

Basically, you create a temporary file with the content in your application, create a DataObject out of it, perform the DoDragDrop and then delete the temporary file.

Here are two snippets (one for WPF, one for WinForms) to show you this. Just call them somewhere (for example in a MousDown event of on a button click).

WPF

private void DragText()
{
    // Create temp file
    var tempFilePath = Path.Combine(Path.GetTempPath(), String.Format("{0}.txt", "test"));
    File.WriteAllText(tempFilePath, "Hello world!");
    // Prepare the data object
    string[] files = { tempFilePath };
    var data = new DataObject(DataFormats.FileDrop, files);
    data.SetData(DataFormats.Text, files[0]);
    // Perform dragdrop
    DragDrop.DoDragDrop(this, data, DragDropEffects.Copy);
    // Delete the temp file
    File.Delete(tempFilePath);
}

WinForms

private void DragImage()
{
    // Create temp file
    var tempFilePath = Path.Combine(Path.GetTempPath(), String.Format("{0}.jpg", "test"));
    pictureBox1.Image.Save(tempFilePath, ImageFormat.Jpeg);
    // Prepare the data object
    string[] files = { tempFilePath };
    var data = new DataObject(DataFormats.FileDrop, files);
    data.SetData(DataFormats.Text, files[0]);
    // Perform dragdrop
    DoDragDrop(data, DragDropEffects.Copy);
    // Delete the temp file
    File.Delete(tempFilePath);
}