The only fool proof method is to not show any of your images on line. That is a draconian approach, but it is the only way to prevent your images from being leeched.
That said, I do host some of my images on line, and dealing with people like john_hougang is just something we have to deal with.
However, though nothing much can be done, if we come across any such incidents, blatant or now, we need to act on it. I thank the person who alerted me of the john_hougang character on SB.
In addition to working with the websites and hosting services to remove the leeched images, we should try our best, if possible, to identify the person who had committed this act. Once identified, this person should be outed and branded.
We did that to some, remember the guy who leeched the pictures of aircrafts/airlines? Just to name one out of many.
Else, there is nothing much we can do, but we have to do what we can.