If you post pictures to Flickr, you better be careful about selecting the options for your license. You might be allowing a company to use it for commercial purposes and they can do anything they want with it.

A Dallas family has sued Australia’s Virgin Mobile phone company, claiming it caused their teenage daughter grief and humiliation by plastering her photo on billboards and Web site advertisements without consent.
[…]
Chang’s photo was part of a Virgin Mobile Australia campaign called “Are You With Us Or What?” It features pictures downloaded from Flickr superimposed with the company’s ad slogans.
The picture of 16-year-old Chang flashing a peace sign was taken at an April church car wash by Alison’s youth counselor, who posted it that day on his Flickr page, according to Alison’s brother, Damon. In the ad, Virgin Mobile printed one of its campaign slogans, “Dump your pen friend,” over Alison’s picture.
The ad also says “Free text virgin to virgin” at the bottom.
[…]
People who post photos on Flickr are asked how they want to license their attribution. The person who posted the photo of Chang chose a sharing license from Creative Commons that allows others to reuse work such as photos without violating copyright laws, if they credit the photographer and say where the photo was taken.

I suggest you only publish photos you don’t mind losing control of because eventually anyone could get a hold of them and do anything they want with them.