It took me a while to realise a) using a reference wasn't 'cheating' and b) making use of all the tools available also wasn't 'cheating'! Sometimes when using photo refs for portraits I'll do like you said, photograph or scan the work in progress to pin point where it's off - I put it in photoshop and overlay it on the reference. It's interesting to see the regular things I do wrong when trying to get a likeness - the main one being making noses too long, which then throws the whole face out. I was surprised to see 99% of the time I have the eyes spot on, which is encouraging. I know some people grid the page and photo and do it that way - in fact I've seen loads of people on Portrait Artist of the Year doing that technique.
I mean, why trying to draw Jensen, I'll use anything I can to pin that stupidly perfect face down. 😂