Using SRCSET with WordPress Images and Featured Images

[WaxMikhail]

Howdy Folks,

I have been trying to get SRCSET to load in images for different device sizes.

My understanding is that when the device width or window width changes, that SRCSET will ONLY load the URL of the corresponding size.

I can see the URLs generating for each image, as well as the sizes. These are all actual images and they link properly to the correct sizes:

This is great! The issue is, I haven’t been able to produce, on any device, proof that the browser is loading anything other than the original (large) image. In other words, that anything is happening with the other, mobile optimized sizes. If I open or save the image in question it’s always the original one. The smaller sizes of image appear not to be utilized at all.

So: is there a Javascript component, or otherwise some kind of configuration setup I’m missing? Something to hook into in WordPress? I’m using a custom theme but notice the same using TwentyFifteen. Is there something I need to register in the functions file? I’m writing this after a lot of research and am still totally stumped what step I’m missing.

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