<Grid AllowDrop="True" Background="Transparent"/>

using System;
using System.Runtime.InteropServices;
using System.Windows;
using System.Windows.Input;
using System.Windows.Interop;
using IDataObject_Com = System.Runtime.InteropServices.ComTypes.IDataObject;

namespace WpfApp2
{
    [StructLayout(LayoutKind.Sequential)]
    public struct Win32Point
    {
        public int x;
        public int y;
    }

    [ComImport]
    [Guid("4657278A-411B-11d2-839A-00C04FD918D0")]
    public class DragDropHelper { }

    [ComVisible(true)]
    [ComImport]
    [Guid("4657278B-411B-11D2-839A-00C04FD918D0")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface IDropTargetHelper
    {
        void DragEnter(
            [In] IntPtr hwndTarget,
            [In, MarshalAs(UnmanagedType.Interface)] IDataObject_Com dataObject,
            [In] ref Win32Point pt,
            [In] int effect);
        void DragLeave();

        void DragOver(
            [In] ref Win32Point pt,
            [In] int effect);

        void Drop(
            [In, MarshalAs(UnmanagedType.Interface)] IDataObject_Com dataObject,
            [In] ref Win32Point pt,
            [In] int effect);

        void Show(
            [In] bool show);
    }

    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private IDropTargetHelper ddHelper = (IDropTargetHelper)new DragDropHelper();

        private void Window_DragEnter(object sender, DragEventArgs e)
        {
            e.Effects = DragDropEffects.Copy;
            e.Handled = true;
            Point p = this.PointToScreen(e.GetPosition(this));
            Win32Point wp;
            wp.x = (int)p.X;
            wp.y = (int)p.Y;

            ddHelper.DragEnter(new WindowInteropHelper(this).Handle, e.Data as IDataObject_Com, ref wp, (int)e.Effects);
        }

        private void Window_DragOver(object sender, DragEventArgs e)
        {
            e.Effects = DragDropEffects.Copy;
            e.Handled = true;
            Point p = this.PointToScreen(e.GetPosition(this));
            Win32Point wp;
            wp.x = (int)p.X;
            wp.y = (int)p.Y;

            ddHelper.DragOver(ref wp, (int)e.Effects);
        }

        private void Window_DragLeave(object sender, DragEventArgs e)
        {
            e.Handled = true;

            ddHelper.DragLeave();
        }

        private void Window_Drop(object sender, DragEventArgs e)
        {
            e.Effects = DragDropEffects.Copy;
            e.Handled = true;
            Point p = this.PointToScreen(e.GetPosition(this));
            Win32Point wp;
            wp.x = (int)p.X;
            wp.y = (int)p.Y;

            ddHelper.Drop(e.Data as IDataObject_Com, ref wp, (int)e.Effects);
        }
    }
}

<Window x:Class="WpfApp2.MainWindow"
        ...
        AllowDrop="True"
        DragEnter="Window_DragEnter"
        DragOver="Window_DragOver"
        DragLeave="Window_DragLeave"
        Drop="Window_Drop">
    ...
</Window>

BitmapSource bitmapSource = null;
int Xpos = 0;
int Ypos = 0;
var stream = e.Data.GetData("DragImageBits") as MemoryStream;
if(stream == null)
    return;
using (BinaryReader reader = new BinaryReader(stream, Encoding.ASCII, true))
{
   // Чтение заголовка
   reader.BaseStream.Position = 0;
   int width = reader.ReadInt32();
   int height = reader.ReadInt32();
   Xpos = reader.ReadInt32();
   Ypos = reader.ReadInt32();

   // Получение исходного изображения
   reader.BaseStream.Position = 24;
   byte[] data = reader.ReadBytes(width * height * 4);
   PixelFormat pixelFormat = PixelFormats.Pbgra32;
   int stride = 4 * ((width * pixelFormat.BitsPerPixel + 31) / 32);
   bitmapSource = BitmapSource.Create(width, height, 96, 96, pixelFormat, null, data, stride);

   // Трансформация, поскольку исходное изображение перевёрнуто и отражено
   TransformGroup transformGroup = new TransformGroup();
   transformGroup.Children.Add(new RotateTransform(180));
   transformGroup.Children.Add(new ScaleTransform(-1, 1));
   bitmapSource = new TransformedBitmap(bitmapSource, transformGroup);
}