> A single combination of web browser and operating system can be used on both low DPI displays and high DPI displays.
If the image is wider than the window, you get scroll bars; also, browsers can resize. It's not the server's job. We don't have a bandwidth shortage. We have a decently flexible content shortage. If you know it's a mac or a PC, you know it's got a desktop range of pixels. Likewise any particular smartphone. There's no mystery here worth noticing.
Don't resize images with the viewport. That's very annoying. They should reflow with the window according to the browser's settings. If you set a constant width, then you're asking for scroll bars if the window can't fit that width. This all works very well. It has for a long time. Stop trying to make it not work.
Just because you can do something, doesn't mean you should do something. You could make both the text and the background black -- but you wouldn't, right? Because it's highly unfriendly, to say the least. Well, so is locking the user's browser view to particular widths and heights and sizes and positions. HTML was intended as the content provider; the browser intended to be the content formatter, using only hints -- lines, paragraphs, font styling, etc. The closer you can get to that in web page design, the better web page designer you are, because then the user gets to fit the thing into the window the user wants it to be in.
Every time I run into a page that makes me resize my browser to make the damn thing work, I curse. Every time. Every time some whackjob decides that menus should drop or windows should open when my mouse pointer crosses some object, I curse. Every time I run into some page (like liveaquaria.com's) that won't run its cart or checkout through the usual standard ports and protocols, when everything else from Amazon to the tiniest little retailer and back to EBay will, I try to find somewhere else to shop.
Stop trying to be clever with the page. Instead, be clever with what you put on the page.