Technology is rad, isn't it? I mean, here we are with smartwatches on our wrists with pretty respectable LCD and AMOLED screens. We were using phones a few years ago that didn't have many more pixels than our watches have. Might as well put those pixels to use showing something pretty, like images from 500px. You can do that with Mural Watchface.
This watch face plugs into 500px to bring up the most popular images on the site. Simply pick the one you want in the phone app, and push it to the watch. On top of the image you get small circular overlays with the time, date, battery level, and weather. You can tweak this display to hide stuff you don't want. Mural Watchface also supports adding your own images to the watch.
The free version of the app only shows the top 10 from 500px, but a $1.99 upgrade pushes that to 40 and allows you to add unlimited favorites (among other things). Note, there is no black and white UI for this face when dimmed. So it's not ideal for AMOLED watches, and it's acting a little buggy on the G Watch R when dimming. The phone settings app is also a bit messy, but it's a quick and easy way to get pretty pictures on your watch. It seems to work swimmingly for most devices.