You may set the BitmapCacheOption.OnLoad
option during initialization of the BitmapImage. This lets WPF close the image file right after loading the image.
var bitmap = new BitmapImage();
bitmap.BeginInit();
bitmap.CacheOption = BitmapCacheOption.OnLoad;
bitmap.UriSource = new Uri(ImagePath);
bitmap.EndInit();
ImageBitmap = bitmap;