Depends what its for, to be honest? Is the photo of them? If so they have as much right to your image of them as you do.
I really think that some photographers are taking the proverbial charging £25 for event photos. If you want to take photos of me, fine, but if you want to charge people for them then I want my modelling fee. £200 please – pay up.
I love this one. You get your lawyer and I'll get my lawyer and let the legal chaps sort it out, eh?
Re the OP, the letter sounds polite enough but I wouldn't expect the picture to be removed. If the picture has any value you should look at a legal way to recover money.
The security issue is interesting. How can you prevent theft of an image from the internet? Impossible I think.
I need the internet as a shopwindow for my pictures, and I have chosen flickr for this. I accept that pictures will be taken without permission and live with it, but all the pictures are a lower reolution and carry a watermark with my web address. This, however, didn't stop one site poaching the pic and cutting the watermark off before publishing it on their own page without crediting me, I found a further 800+ photos which the site had been using. They are currently being sued.
I need to publicise my pictures to sell them and accept a number will be stolen, but I make sure the photos are not the greatest resolution.
I have a photo of a guy taking a picture of one of my display prints which don't carry watermarks!!! FFS!
Good luck.