I think to exploit anyone, whether for fun, profit, or enticement of others, whether to their knowledge or not, is wrong.
Even if one can reasonably rationalize that "what a person doesn't see or know doesn't hurt them", it still doesn't take the blemish away, nor the moral implications involved.
I'm also happy to see that others are courageously displaying their dislike of people posting pictures of their wifes and girlfriends, etc, knowing it sexually arrouses people here, is masturbative material for many, and that they (more often than not) request more.
I find two problems with that:
1.) It means you've created pornography and are cheapening the pictures by sharing them with people who could never value them as much as you could in being the husband, boyfriend, lover, etc, of the beautiful creature you took the pictures of. I'd want to safeguard that and cherish it, not pass it around like a peace pipe and turn it into something perverse by involving third parties. Stroking your ego by sharing your "catch" with your fellow fetishists isn't worth it, and is, in it's own way, degrading.
2.) Provided the woman is unaware of these pictures or that there is no consent for sharing, you've violated, to some extent, her privacy. A man wouldn't want pictures of his mother on the internet knowing men are lusting after her image, and in the same way a man shouldn't want his woman being seen under the same conditions. It should be awkward and uncomfortable. The fact it is not for many of the contributors here and that no one seems to second-guess what they're doing, is a little revolting. Just knowing this material is viable and a commodity in this community, and I see people begging for more and making requests out of place and sometimes out of line, perhaps forgetting who the woman is, is something I'm not proud of the community for, either.
Its one of the darker sides of the fetish that often has no bounds and loved ones are exploited, whether willingly, through cajoling, or without their knowledge.
So yes, I feel taking pictures without anyone knowing should be avoided, even if only out of respect for that person. Its just one of those grey areas where you have to decide whats more important- what you want as a fetishist (which involves selfishness), or safeguarding that person's privacy and dignity, whether they're aware of it or not (a good deed and a test).