Commercial use requires 'releases' - editorial use doesn't. Stock photos can be sold for commercial (eg, marketing) or editorial (ie, journalistic) use. You'll have more opportunities to make cash if your photos are available for both, but photos containing people or property (including branding and logos) need signed releases to be sold commercially.
As search engines have become more prominent, some affiliate marketers have shifted from sending e-mail spam to creating automatically generated web pages that often contain product data feeds provided by merchants. The goal of such web pages is to manipulate the relevancy or prominence of resources indexed by a search engine, also known as spamdexing. Each page can be targeted to a different niche market through the use of specific keywords, with the result being a skewed form of search engine optimization.