Flutter Image and AnimatedSize widgets

In my application I'd like to render the image with its original height and width. I can have images with different size, so I cannot put explicitly the parameters in the Image widget. The image is inside an AnimatedSize widget.

AnimatedSize(
    alignment: Alignment.topCenter,
    vsync: controller,
    curve: Curves.fastOutSlowIn,
    duration: Duration(milliseconds: 1500),
    child: Container(
      alignment: Alignment.topCenter,
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: document
      ),
    ),
  );

In the code above, the image is in document. While the image is loading, the Container changes its size. Meanwhile, the AnimatedSize expands because of that. This is an undesired behaviour for me. How can I solve this problem?

Thanks a lot.