Its a comic book...they found all sorts of ways to try and make it make sense since to the reader they looked almost identical. One time it was that whenever Superman was in pictures he would vibrate ever so slightly so they couldn't focus it right or something. It doesn't have to make sense it just needs to be enough to have people turn to the next page.
In truth the glasses are more than enough. I look very different in glasses than I do without them. They frame my face differently. If you watched Supergirl Kara's nose looked different with glasses than without. The smallest change in features of the face can make profound differences. Same with hair. The extra sauce is how one carries themselves. Superman should stand differently than Clark. I thought Superman and Lois did this great. Clark looked like your average dad in Smallville not super strong and hardly noticeable sometimes even somewhat meek. Superman (thanks in part to that massive suit) looked massive and godlike...he stood tall and confident. Everything akes them look completely different.
But ultimately, my favorite explanation was that people didn't see it because they didn't want to see it. No one wanted to believe that Superman was just living amongst them so their brain never made the connection. Even Lex was so arrogant that he never could imagine it even in the stories where he grew up seeing Superboy in Smallville. Lois had to know, that is why she is always trying to figure it out and why she often does.
I never agreed with people that said Christopher Reeve's Clark Kent and Superman looked exactly the same. As Clark, in addition to changing his posture, slouching, changing his voice, the look of his face also worked, largely because of the glasses. No pun intended. Reeve also seemed to raise his eyebrows up showing wrinkles on his forehead. Almost as if looking older?
Then when Superman makes his debut in the first movie, he has a whole different demeanor. He has self-confidence, this voice and very commanding presence. Just everything opposite of Clark Kent. It was amazing.
To me, none of the other Clark Kent portrayals match up Reeve's performance in terms of fooling people with the disguise, or literally just the glasses. I'll point out that in real life, wearing glasses to fool other people doesn't work for every single person.
And here's further proof that the glasses can work. Many years ago at uni, I wore contact lenses, but one day I wore glasses. After stepping out of the restroom once, a girl I knew walked RIGHT PAST ME. After a few seconds, I called her name from her back, and then she turned and said my name in surprise. She said "Gu3??" As soon as she heard my voice, she knew it was me. But she told me she didn't realize it was me with the glasses.
I felt kind of proud of that.
Back to the other Clark Kent portrayals. I like Hoechilin but I have to admit he didn't look or seem all that different when he was Clark Kent. He had the same voice. I felt like there was no way Lana or Kyle couldn't have hinted. Same with Dean Cain. That distinct voice. It was season 2, Clark was dating some woman that hated Superman but liked Clark Kent. Lois was in the scene. Superman had a scene with these two in the city, he flew away and 2 seconds later, he showed up as Clark Kent, and no one suspected a thing.
