Letting of Some Steam copied images

What’s really starting to P**s me off is other webmmasters stealing my images and even site logo’s, okay some of the images contain casino, poker, bingo e.c.t company logos but I have changed them to look better and for that reason they get copied, I finished a new site upgrade about 4 weeks ago & already I am seeing them robbed.
Is there nothing we can do to stop this.