Regarding the second answer:
If an act that does not harm anyone is not considered immoral, then is reading a person’s diary without their ever knowing about it not an immoral act?

Or—if someone takes an immodest picture of a man/woman without their knowledge and without sharing the picture, is that not an immoral act?

It’s hard to accept that these actions harm the person, since they will never feel that they were done. On the other hand, it’s hard to define them as morally neutral acts.

There are harms even if I don’t know about them. Someone puts poison in my drink and I die. Is that moral? I didn’t know about it. If there are things I do not want done to me (for example, that you be exposed to my diary), then it is immoral to do them even if I don’t know about it.
I didn’t understand the question about an immodest picture at all. You could just as well have asked about a case where you pass it around and publish it in the newspaper but I don’t know about it. And on the other hand, why is it different if you see the picture than if two or three people see it?!

Can the Rabbi sharpen the point about what the moral problem is in photographing a woman, without publishing it, without her knowing?
In what way does it harm her?
And is there also a moral problem with looking at women in the street or at the beach (assuming they do not notice), and if so, why?

Without beating a dead horse, and if the Rabbi finds that the discussion is repeating itself I’ll of course understand if there’s no response, but I’d like to respond to this paragraph:

"***There are harms even if I don’t know about them***. Someone puts poison in my drink and I die. Is that moral? I didn’t know about it. If there are things I do not want done to me (for example, that you be exposed to my diary), then it is immoral to do them even if I don’t know about it."

True, there are indeed harms that happen without your knowing about them, but there are also actions done without your knowing about them that do not constitute harm.

For example—is desecrating the grave of a solitary person down to the dust (and let’s assume the grave is in an isolated place that people do not visit) an act that is not immoral? And even if the Rabbi explains why there is a harm that I am not aware of, can one not still conceive of an ugly act that does not harm any person?

The harm is that a woman does not want pictures of her to be in other people’s hands. The distress she feels when she finds out is only a result of the fact that this very state of affairs is undesirable to her. I don’t see what is unclear here.

Of course there are such things. If someone stands on one foot and I don’t know about it, that doesn’t harm me.