Not likely. You do whatever you can, put watermark or signature, publish small picture and so on.
But chasing your pictures over the net is full time job, and probably wasting of time, and after all what can you done, writing mails to people all over the world to remove them from their sites, blogs or facebook accounts? Will you sue someone that put 800 x 600 picture on his blog, lives in some distant part of the world and not even speak your language??
That is naive, from my point of view. If someone download it and print it to put it on the wall you will not even know that. As I wrote - commertial use is something else, but this is much easier to detect than sporadic use of internet comunity. After all there is one company in Israel, can't rememr right now the name, google it, which can protect your picture even if someone edit it, change it or use only part of it or even as a tumbnail. But this is not free, so if you value your pictures soo much, use their services, invest in your protection.