In that case no-one has violated your privacy - your wallpaper is private, so friend A didn't, and you invited friend B over, so they definitely didn't.

I would entertain the idea that friend A is being a bit of a douchebag by painting stuff all over your house without you asking them to, but if you subscribe to that thought process you'd already be running an ad-blocker and this scenario wouldn't ever occur in the first place.

Having to use an ad-blocker for this purpose is a band-aid for a much deeper problem. Running a website isn't free and I want to support them by not blocking their ads. But when the ads are part of a scheme that targets my private and personal information, I'm no longer willing to hold up my end of that contract.