In the hopes of finding out the rendering engine Snapito used, I tried http://snapito.com/?url=http%3A%2F%2Fwhatsmyuseragent.com%2F ; however, that seems to hang forever. I would chalk that up to heavy load from HN, except that other pages seem to work just fine.
:-) I use wkhtmltoimage but I’m considering a move over to PhantomJS it’s a known bug that if a page contains a missing resource which 404s then the whole thing 404s. Hence why I’m considering PhantomJS as it’s at least a lot easy to program error detection etc.