Images are embedded in the pdf regardless of whether their element or a parent element are set to display:none;
The previous version of Prince did not function this way. A workaround is just to set the content attribute of certain images to content:"", but it would work better without having to do it this way.
Essentially, when parsing through an xml and pulling certain elements out to create a pdf, *ALL* images are embedded in the pdf regardless, resulting in (depending on the number of graphics and their size) a very large filesize, even if the pdf is only several pages long. Of course, the images follow the correct .css rules, and don't display, but they are embedded into the pdf.
Is this the way it should function?

Thanks for reporting this issue, we will investigate it and attempt to fix it for the next release.

Just to follow up, this issue has been corrected in Prince 5.0 beta 2.

Thanks again for reporting it!