Upload & Sell: On
Unless you're a professional photographer who regularly licenses/sells work, this is likely a mountain over a molehill. Hiring a copyright attorney for a photo that would likely have netted you a few hundred dollars IF it is yours and IF it wasn't taken from a photo hosting site that in the small print reduced your rights as a condition of using the site? With 5 million amateur photographers taking thousands of photos a year, the chances of you getting a unique shot of anything but your own child is pretty slim. I know that pride in our work can lead to bruised feelings if we believe it is being misused, but it seems to me that pursuing this matter beyond what you've already done would be pretty much a waste of time.
My friend who does regularly license/sell his work never posts anything online that is large enough to be used by a magazine and all images have a watermark on them. And his site is set up in a way that you can't copy images. If you want to become a professional in this business you might want to think about how to protect your work as my friend does...