Responsive images
Serving the appropriate image to users based on the particulars of their device and environment has always been a tricky problem. This problem was accentuated with the advent of responsive web design, the very nature of which is to serve a single code base to each and every device.
The inherent problem of responsive images
As an author, you cannot know about every possible device that may visit your site now or in the future. Only a browser knows the particulars of the device viewing a website: its screen size and device capabilities, for example.
Conversely, only the people making the website know what versions of an image we have at our disposal. For example, we may have three versions of the same image: small, medium, and large; each with increasing dimensions to cover off the anticipated screen size and screen density eventualities. The browser does not know this. We have to tell it.
To summarize the conundrum, we, as the website authors...
