It's interesting you say that because it actually was an image of a sprinkler head. I obtained the image from a third party website where no copyright notice was visible on the smaller-than-original image. I was notified of infringement of the original large image with the copyright text on it.
The company I web mastered for is the owner of the website, I did their website for free since they are a very small company. They had no idea about it, although apparently it is ultimately their responsibility. It was used on the homepage of the website which had nothing but contact details such as phone number, and a short 1/4th of a page description of the business. It was a single-page website with only one image, which almost no one knew about outside the company. Certainly, web crawlers found it or some other bots and not human searchers.
I've read as much as I can here, and am pressured for an answer right away as the web master is seen as the responsible party. Of course, ultimately the owner of the business is liable even though they are innocent victims just as everyone is due to the extortionate amounts of money demanded for measly images. Clearly these people are capitalizing on a lawful venue for an extortion scheme going beyond reasonable demands, what is extremely unclear to me is how many single-image cases like this lose in court, and what the damages usually are. If there is any practical risk of losing upwards of $2,000, does it really make sense not to settle?