Recommendations for best performance for images in a listview?

I have a collection of items/documents (in Firebase). In FlutterFlow, I am creating a listview from this data, the card include an image. Currently I have referenced the full network address. e.g. https://somesite.com/someimage.png

There is a noticeable download time when entering the page for the first time.

What's the best way to do this? Is it to use network and cache the image. Or to upload all images as local assets - if it's this, how do I store the reference, e.g. to assets/images/someimage.png ?

Or is there a better way?

Many thanks,
Jon.