Is it possible to set the equivalent of a src attribute of an img tag in CSS?

Question

Is it possible to set the src attribute value in CSS? At present, what I am doing is:

Answer 1

Just use HTML5 :)

<picture>
    <source srcset="smaller.jpg" media="(max-width: 768px)">
    <source srcset="default.jpg">
    <img srcset="default.jpg" alt="My default image">
</picture>