I told the people who had taken my work that I owned the copyright.
They were pretty swift in removing it.
It's one of the pitfalls of the internet. There's no real way of safeguarding your work. Take no notice of Apostle Jack, sometimes you have to stand your ground, but most of the time, there's no real need to fight as such, you just need to point out that copyright theft can be costly and that usually dampens their spirits.