I sometimes post photos on my blog, like when I'm blogging about food. I've been shrinking the huge pictures my phone takes down to a size that fits more reasonably in a browser window -- my browser window, so far -- because I don't want my posts to require a huge window. Recently I've noticed that the platform I use (Dreamwidth) now has some degree of responsiveness; if I make a Chrome window smaller it scales the photos too, and my posts even look fine on a phone. This was not always the case, and is still not the case in Firefox for some reason. (I haven't tested additional browsers.)
That some sites and/or browsers do scaling suggests I could use higher-resolution pictures, but some browsers don't scale so I don't want things to be too huge. In addition, bandwidth might still be a concern; not everybody has fiber or a beefy data plan, after all. And on the proverbial third hand, there are now high-DPI displays on which the photos I'm using might be tiny (I don't have direct knowledge).
Putting all this together, what are current good practices for photo sizes on blog posts? Should I keep doing what I'm doing, which is to scale down the width to under 1000px (generally ~800px)? How do I trade off large high-res displays on the one hand and smaller displays with browsers that don't auto-scale on the other?
Note that I'm not talking about special photos where I might especially want high-res (like that gorgeous sunset photo taken on vacation or the like). In that case I'd make a higher-res version available behind a click, so it's opt-in. Nor am I asking about print publications where higher-res is important for production values. I'm asking about "ordinary" photos included in blog posts.