i think its the lax in attitude towards certain aspects of being a Jew that we are seeing more of recently. this chill out and relax attitude i think is coming from the american society. people keep saying here that stop making up chumros while in reality its halacha and telling themselves that its only a chumra and only lakewood does it. just because you feel for whatever reason this and that is not for you doesnt make it a chumra.
I never heard of a HALACHA that said a properly dressed women being seen in a photograph is halachically assur. Even if seen by people who don’t know her. Please provide a source if you are going to make a sweeping statement like that.
Now, looking at an untznius picture is a totally different ball game. If you see problematic pictures on OS, either alert the moderators, or stop going to the site. As you said, for you its only to satisfy your curiosity to see who is engaged. Do you realize how easy that is to lead to loshon hora? You mention to your neighbor “Did you see who got engaged? Its on OS.” And she might respond “I cant imagine the kind of guy who would want to marry her!” I think that is potentially MUCH worse.