Law wise there are a couple of things to consider. First the subject of the image and second the image itself.
There are some subjects that are already under copyright protection, things such as company logos, iconic bottle shapes or landmark buildings. If you want to use these you would have to get permission of the copyright holder.
Then you have the rights of people in your images, ideally you should be getting them to sign a contract that allows you to use them in shots you sell.
Assuming you have all the rights to distribute images of the subject then you have the copyright of your images which is pretty much down to you and how you want to license use of them.
Here is a link to a freelance journalist site with some information and further links http://www.londonfreelance.org/feesguide/phcoptxt.html
These stock photography sites have information about model release forms.