ImageHelper.cs

using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Windows.Media.Imaging;

namespace SlideShow;

public static class ImageHelper
{
    public static BitmapSource ToWpfBitmap(this Bitmap bitmap)
    {
        using MemoryStream stream = new();
        bitmap.Save(stream, ImageFormat.Png);

        stream.Position = 0;
        BitmapImage result = new();
        result.BeginInit();
        // According to MSDN, "The default OnDemand cache option retains access to the stream until the image is needed."
        // Force the bitmap to load right now so we can dispose the stream.
        result.CacheOption = BitmapCacheOption.OnLoad;
        result.StreamSource = stream;
        result.EndInit();
        result.Freeze();
        return result;
    }

}