If you use email on a near constant basis, I'm sure over the years you've built up quite of a collection emails which contain pictures too. Lost Photos is an app for Windows and Mac which lets you find all the photos that have been buried deep inside your email accounts.
I just downloaded the app, which is completely free, and put in various email accounts I have had over the years. It was amazing to find pictures which are years old that I had completely forgotten about, they actually bring back memories. At the same time some of them made me cringe, but it was fun nonetheless.