<picture>
<source srcset="img/awesomeWebPImage.webp" type="image/webp">
<source srcset="img/creakyOldJPEG.jpg" type="image/jpeg">
<img src="img/creakyOldJPEG.jpg" alt="Alt Text!">
</picture>
.no-webp .elementWithBackgroundImage {
background-image: url("image.jpg");
}
.webp .elementWithBackgroundImage{
background-image: url("image.webp");
}