I'm downloading a website using HTTrack, it's downloading all the content but
it doesn't download images in <source> html <picture> elements

For example

<picture>
    <source srcset="thumb1.png" media="(min-width: 1200px)">
    <source srcset="thumb2.png" media="(min-width: 992px)">
    <source srcset="thumb3.png" media="(min-width: 600px)">
    <source srcset="thumb4.png" media="(min-width: 320px)">

    <img src="img.png" />
</picture>

In the example above, HTTrack downloads the img.png but it doesn't download
the source thumb1.png, thumb2.png, thumb3.png, or thumb4.png

Is there some settings I should enable to download the source elements in the
<picture> elements ?
Thank you.