If you put your images up on the web, you are frontierland, one where the law is vague, can be challenged and in time you will undoubtedly be approached regarding the use of an image. I get approaches from businesses who have seen my images on Flickr (the most recent one being a State-wide tourism map of popular places e.g. Victoria's Bells Beach) and once I see what they are involved in, I usually do agree, providing I am properly credited and I can see the finished art online. So long as they ask/approach you. Considering the uber-popularity of set ups like Getty Images, photographers in Flickr should count their blessings they are being singled out for attention, even if more often enough they are not remunerated.