HTML-Pages using the Picture-tag seem not to be supported. The different Images
referenced in <scrset> are not downloaded and changed. Only the
<IMG>-Reference is handeled correctly.

Short example:
 <picture class="img-responsive" data-alt="" title=""
data-default-src="/website/var/tmp/image-thumbnails/10000/10867/thumb__contentfull/Evolution001_1.jpeg">
	<source
srcset="/website/var/tmp/image-thumbnails/10000/10867/thumb__contentfull/Evolution001_1~-~350w.jpeg
1x,
/website/var/tmp/image-thumbnails/10000/10867/thumb__contentfull/Evolution001_1~-~350w@2x.jpeg
2x" media="(max-width: 350px)" 
<img class="img-responsive" alt="" title=""
src="../../../../../website/var/tmp/image-thumbnails/10000/10867/thumb__contentfull/Evolution001_1_-_350w.jpg"
/>
</picture>