MediaHound

Hi Luc,
One of the main reasons why we decided to use a watermark is because it discourages people from using our photo gallery to host pictures of their Paris trip, or pictures of their wedding, etc. We can afford to host the banana pictures for free for our members, but we don't have all the space in the world for all the pictures in the world.
And so now that we are insuring the photos are mostly on topic of bananas or plants, another reason why it is useful is because the watermark is a way for people that see the picture is hosted at Bananas.org. When people see this watermark posted to threads at other sites, for example, they will know about our site and come and check us out and maybe join as a new member. It is "viral marketing". It is a way for our community to be able to sustain growth on it's own. It does this job very well, I might add. And the more members we have, the more valuable the site becomes to the existing members, and the more networking that can be done.
And like Harvey stated, it also helps discourage the photos from being used by other sites or print publications as their own images. When Joachim made his book, for example, and he wanted to use some of the photos for it, he needed to contact us and our members for the original photos. Another example - our member Jordon (jnstropic) (the guy on the left in my current avatar) has been growing Ae Ae for over 40 years. His pictures of the plant were some of the first online and have been used by many websites to describe the plants, with no credit back to him as the photographer. Jordon now watermarks all his images after the rampant use of his unwatermarked ones.
I hope this sheds some light on it for you! As you can see, there are several reasons why! Best regards.