Isn't there something going on with digital scrubbing or DNR on these blu-rays? Especially Trek III & IV. The picture seems really off, like it was sliced out and pasted on top. I noticed this when I played them too, but it's clear in these photos.
All of the Star Trek original and next gen blu ray releases (apart from Abrams Trek) had DNR and edge enhancement applied to one degree or another. The best looking transfers are TMP and TWOK, both of which were brand new masters, TWOK itself recieving a fairly extensive cleanup. Both appear to have a light application of DNR which isn't really obtrusive or unpleasant and both have a fairly convincing film-like appearance. Trek III has noticeably heavier DNR but its main problem seems to be the edge enhancement which leads to that "cut out" look, though I still think on balance its a fairly good transfer and at times clarity and depth are startling. Trek IV is a mess though, both DNR and edge enhancement are totally over the top, but IMO the worst of the lot is TUC which is so scrubbed and processed that in some scenes, entire facial features are wiped away and faces lose their eyes or nostrils and even mouths!