[DiapDealer]

Make sure you are opening the OPF file of the epub in PageEdit from Sigil. Otherwise you are strictly in a single xhtml file editing mode. None of the images in the epub will be available for PageEdit to insert otherwise. I'm not 100% certain that it's the same with the other two you mentioned, but I suspect it might be. We've got a request to disable those functions that aren't available in single-file mode, but it will be in the next release.

EDIT: in case I wasn't clear... the image has to exist in the epub's archive already for PageEdit to be able to insert it into a file (and PageEdit has to be launched in multi-file mode by clicking the Launch External Editor button with the opf file open in Sigil). PageEdit doesn't have the ability to add/remove files from an epub regardless of how it was launched, so it can't be used to add external images to the epub.