My wife uses gmail. I don't and have never had a google account, have never uploaded a photo to them or to any other web photo service. One day my wife asked me "What's that picture with your email, the Causeway?"
A long time ago, before Google bought them, I created a YouTube account and uploaded a couple of time-lapse videos of my commute across the Lake Pontchartrain Causeway. And my contact email for that account was my yahoo email account. So apparently, when I sent my wife an email the Google gophers went scampering for an avatar, and having nothing else took the sample still for one of my YouTube videos and pasted that at the top of my incoming email.
I'll leave it to others to speculate on just how this could have gone wrong. I could probably fix it since my old YouTube account has apparently been grandfathered in to a g+ or whatever account now, but I'm leaving it as is to remind me never to trust them with anything sensitive.