We have a few images stored in an assets folder in the src of our React app that we reference. These are small things like icons that are compiled with the React app.
The rest we have in blob storage and reference those urls.
There would be some serious size limitations on any files you’d be bundling up with the application. But if your app is meant for a single store only I’d imagine you can still use the Shopify CDN ; just copy the URL from the Admin and reference it in your app. If your app is meant for multiple stores you’d probably need to look into something like blob storage for your image assets needs.