Memories is a new app that lets you view photos from years gone by on your iOS devices, either inside of the app, or with its widgets.
Memories supports all three widget sizes, and they will each show a single photo from previous years. It won't just show the one photo for the whole day though, as it cycles through multiple photos throughout the day.
A lot of these types of apps exist, where you can go back in time and experience old memories. But personally, I know I'd never actually ever use them. That's why I like these widgets, since I can put a widget on one of my home screens, and my phone can remind me of various memories as I use it.