@fuaho; You said;

"Why did you post your images without an embedded, impossible to remove copyright notice?"
"For even better protection on works that you would like to sell, embed a digital watermark through a service like digimarc in addition to the copyright notice."

The big problem here is that "invisible, embedded" copyright notice will do NOTHING to prevent the type of image theft just experienced.  The images will have still been ripped and would still have appeared on the other site.  What these services do is they provide a method to PROVE that you are the copyright holder.
Some provide online tracking services that do give some method of notification of use however they are not perfect.  Nor do any of the embedded copyright notices help once the image has been printed and sold.

You also said: **"It is not up to Renderosity to put a copyright notice on works you post here as they are your works, not Rendos"
**Agreed....although it should be in Renderosity's interest to help minimize image theft from its members and its site....If people just come here to rip the works of others, at some point people will stop uploading their work.

In youth, we learn....with age, we understand.