Serving smaller images for smaller screens

Hi,

With all the different sizes EWWW creates, it was 100% sure it was sending to the page the right image using probably JavaScript to determine the screen size.

I.e. an image of 600px that only shows at, let’s say, 150px would not send the 600px image, but rather the 150px one, to reduce bandwith and especially the download time (and prevent the user from using a lot of data charging a big image then reducing it)…

But I’m not so sure anymore: just did a test on two sites (one with the plugin Force Regenerate Thumbnail that someone else installed and no cache plugin and another one without this plugin and with W3Total Cache and Autoptimize) and they both send the same image (at least in Chrome on my desktop, can’t see the code on a real device) no matter the screen size…

Am I missing something or it really always send the same image and the different sizes are just if we choose thumbnail, medium, full, etc (though there are images with specific file size and more than just the few predefined WP formats)…?