If I watch a movie, then draw a near perfect likeness of the main character from my very good memory, put it on a tshirt and sell the t-shirt. That is grounds for violation of copyright if the source isn't yet in the public domain (not guaranteed but open to a lawsuit).

If I download all content from a website that has a use policy stating that all content is owned by that website and can't be resold. Then allow my users to query this downloaded data and receive a detailed summary of all related content, and sell that product. Perhaps this is a violation of the use policy.

All of this hasn't been properly tested in the courts yet.. large payments have already been made to Reddit to avoid this, likely because Reddit has the means to fight this in court.. my little blog though, fair game because I can't afford to engage.