这是因为GDI +图片类不是线程安全的。 Hovewer您可以通过每次使用锁避免出现InvalidOperationException当你需要访问的图像，例如绘画或获取图像大小：

This is because Gdi+ Image class is not thread safe. Hovewer you can avoid InvalidOperationException by using lock every time when you need to Image access, for example for painting or getting image size:

Image DummyImage;

// Paint
lock (DummyImage)
    e.Graphics.DrawImage(DummyImage, 10, 10);

// Access Image properties
Size ImageSize;
lock (DummyImage)
    ImageSize = DummyImage.Size;

BTW，不需要调用，如果你将使用上面的图案。

BTW, invocation is not needed, if you will use the above pattern.