Image and html files are all documents on the web. Well at least they used to be. If you put an image on the web, you must expect people to be able to view it also without context.
You can decide to not serve them, looking at the referrer. Wanting your image to show up in image search results but not wanting it to be directly opened is trying to keep the cake and eat it at the same time.
If the same amount of people visited the page containing that image, bandwidth would be a lot more with all the page content loading up. Is there good bandwidth and bad bandwidth?
Image author can embed watermarks, credits, branding into images. Make use of the fact the image is out there.
