Updated code for two use cases.

As per __@zcorpans's__ remarks...

The previous proposed amendment of:

    media="(min-width: 640px)"
    sizes="60v"

has been updated to:

    sizes="(min-width: 640px) 60vw, 100vw"

...on the source tag to avoid use of the media attribute.

This amendment affects the following two use cases:

1) Changing image sizes & different image types use case.
2) Changing image sizes, high-DPI images & different image types use case.

Thank you!