Someone keeps using my watch pics

There's a local guy who also buys and sells watches. He follows my blog and will download my pics then show them around trying to sell the watch before contacting me.

I no longer do business with him but he's still doing this. If he finds someone interested he contacts me with a lowball offer. I've told him to stop doing this but he won't.

It makes it pretty hard for me to sell any watches locally because most of the collectors in Cambridge have already seen the watch because of this guy.

Not sure how to stop him from doing this. Very frustrating.

I know it’s overkill but a letter before action threatening copyright theft, injunction and damages for loss of profits.
Hopefully, a firm letter from a reputable lawyer will scare him off.
You might even get the lawyer to send a suitably worded undertaking for him to sign, undertaking not to use, display etc, your photos and, in return for him signing and returning it, you won’t pursue the action?

Damn, why didn't I think of that? Thanks @madjestikmoose 👍