If I don't post something that's my own, what I typically do is a google image search specifically for stock images, which many times have the stock company's logos plastered all over it. Might even add "stock" to the search. You can tell by looking at the URL and the image together to see if in fact it is a stock image. These are images that are intended for use like this, actually.

Otherwise, if you're posting someone else's work, whether or not you're going to be ostracized for it seems to depend on the mood of your audience.
I, for one, do not feel that earning money on another person's work is ethical at all. I've been a photographer for going on 18 years, and I've had to fight tooth and nail to protect my copyright when someone takes it upon themselves to try to either claim it as their own, alter it (even when trying to give credit), or reap benefits from it. That's what permission is for, and even then many times - depending on the photographer - contracts are involved.
Even if you tried to assume the label of "curator", this is really no different than being an artist's distributor. Now, distributors DO get paid, but not 100% of the profits. That gets shared with the creator, because without the creator, you don't have it to share in the first place.