Unfortunately, images from this website are known to have been copied and printed without permission for use in local guided tours and at least one lecture. All that is asked is the courtesy of asking permission, which will normally be granted.
Images have also been used for viewing on other websites - More seriously, in one known instance, two photographs were altered and used in a printed book publication for re-sale. This was subsequently followed up and a royalty payment was made.
In most cases for non profit making ventures, permission will be given to use the web quality images without charge with a suitable credit.
For higher quality images or commercial use, a royalty fee will be requested depending on the specification required. High quality prints can be also obtained from the author, but are restricted to private use unless permission is given otherwise.
Ideally, there should be no need for a watermarked overlay on the photos, but in the real world there has to be to try and protect them from copying; this does restrict the viewing pleasure, but is necessary due to the images being illegally copied and re-distributed.
Since copying was identified, heavier watermarking has had to be introduced to try and prevent this, but can only go so far without obliterating the image completely.