Apple Faces is a simple website that offers some unique wallpapers for your Apple Watch. The site lists a series of wallpapers containing patterns, colors and shapes. The colors tend to match one of Apple's sports bands, while other wallpapers are throwback calculator-watch-inspired creations. Naturally, each of design carves out a spot to display the time and date.
The ability to set your own photos as a watch face was introduced in WatchOS 2.
Once you've saved the photos to your iOS device, you'll need to ensure that the proper photo album is synced to your Apple Watch. I recommend either favoriting the pictures you want to use, or creating a standalone photo album in the Photos app on your iPhone.
Next, sync the proper album to your watch. You can do so in the Apple Watch app on your iPhone, by launching it and selecting the Photos listing. Tap on Synced Album under the Photo Syncing section, then set your preferred album.
You can follow the steps in this post to set a photo, or entire photo album, as your watch face. It can take a few minutes for your iPhone and Apple Watch to sync up; just be patient if the photos aren't showing up right away.