Level 41This one I was rather proud of back in the day of solving Notpron with my husband over skype. It's the only time I felt clever in this entire puzzle and have never really captured that again since. But that's ok, I have 41!
There's not much in the source here, and you're probably starting to miss those levels already where there were a ton of hints, huh? Well, you have all you need here, but a bit of Google might help as well once you have what you need.
You can solve this the hard way, or if you find something in the source, the easy way, depends on if you have an ear for it.
Level 42Unfortunately no reference to HGttG here, bit of a missed opportunity.
Check your source carefully, as usual. No snarky page for trying to go to 52, slightly disappointing. There is a train of thought you can go down that'll get you an extra clue to work with, but it's not necessary to solve it. Google is all you need for this one.
You'll be seeing some familiar stuff in here, so shouldn't get stuck too badly, long as you answer the question.
Level 43I'm going to save you a bit of time on this and explain something about some of these pictures. David's camera...well, let me just quote straight from the book.
"My digital camera is now almost 5 years old; it's always producing a purple pixel somewhere on the right or left side. It's in many pics of the riddle."
Ignore that pixel if you run across it. It's nothing. I bring it up here because it seems to be more noticeable in this one, where there isn't much going on in the picture and with the lack of any other hints to go off of, it looks important.
That said, this is a really dumb one. It took us a long time to solve, not because it was hard, but because of the opposite reason--it was almost too simple. By this time, you're on level 43 of Notpron, you've done some really weird out there crap, and you don't really expect more "unexpected" answers.
Change what you can and search it carefully, that's all I can really say. At least one snarky page that I know of in here.
Level 44You get to do a bit of hands on with the image on this one, but MS Paint is all you really need, nothing fancy like Gimp. Your main hint here is really the title, but you may have to think a bit abstractly.
That's about all I can say without giving the answer away. It's not a puzzle that you're likely to solve immediately upon seeing it, but once you figure out the trick, it all makes sense from there.
Level 45Here we have a pretty interesting puzzle, which does make sense, involves research (but nothing super obscure), and feels really good to solve. One of the better levels in this section of the game, I'd say, which is good because you'll probably be spending a decent amount of time on it.
The page is in no short supply of information. It goes without saying at this point, but check all the usual suspects until you think you have everything, and then you'll want to figure out what they all mean. Doing that shouldn't take too long, and that leaves you with a series of information that is definitely leading up to something, but how do you decide where the next one falls in place? Sometimes the best solution is to map out what you have.
Only other thing I'll say on this one is that the subject of the picture is irrelevant. There's necessary information you have to take from it, but it has nothing to do with a cat. I didn't have this problem myself, but apparently some people did, so I'll just squash that one outright.