Hi Nick, I enjoy keeping an eye of Wetpixel but never post, this topic however is a raw nerve. I have made my living from photography for the past 15 years or so and regularly find my images being use without rights scattered around the web. I used to get myself in a state approaching rage. I once call a lawyer friend who deals in copyright issues and he gave me some great advice as a friend who is a lawyer. The time, costs involved and general aggravation by far out weight the possible remuneration. I have come to the conclusion that there is copyright law and then there is the real world, even if you win, he takes it down and you won the right to say you were right, value? If this is keeping you up at night, it's costing you a lot more than the image is worth, no matter how great the image.
Don't get me wrong, if a major US corporation or publication tried it I would be all over them legally, go ahead hit me I could use the money. It's generally however not that type of entity that steals our images, it the little low life, who cheats on their taxes and always disappears when it's time to pay the tab. Nine times out of ten a polite letter asking them to take down the image works. Then I send a real grubby letter talking about karma and terminal illness (just joking) and let it die, at least it makes me feel better. I did find another way to get at resorts who do this. I contact the large 3rd party travel sites that sell their resort and threaten them, they react very quickly. I had one resort suspended from a few sites for not taking down a stolen image when asked. I never got paid for the image but believe me I caused this guy a whole bunch of trouble, way more then the web usage would have cost him.
I know I'm drifting off topic here, the thread is about inherent copyrights in our images whether implied or stated. However the same feelings and emotions apply, if we can't afford to let things go emotionally when some %$@#$^& steals an image and won't take it down even though we know we are morally right, don't email your images. Unless with huge watermark, warnings in the XML data and a disclaimer. I stopped emailing images a while ago. It's easier to use a flash gallery site like Zenfolio or Smugmug. You only have to post the disclaimer once on the site, I've set it to place a big fat watermark on anything bigger than a thumbnail and because it's flash it makes those right click, "save image as" a lot more difficult. Then just email them a link to the image or gallery.
Nick I wish you the best of luck and I can feel your pain!!! From what I've read you seem to on the right side of this. How about swopping the model release for the (low res) limited web usage rights?