Is my duck egg viable?

After several days of a pair of ducks visiting our pool, I found a single egg on the cement - no nest, no other eggs. I actually thought it was part of a pool toy at first, so I picked it up and then realized it was an egg. I immediately placed it back down where I found it, but I assumed the damage had been done. The ducks didn't visit that day, so I brought the egg inside and put it in an incubator. The next day, I found another egg in a different spot, also out in the middle of the cement, but it was broken. I haven't seen the ducks since.

I have had ducks lay eggs poolside before, but they are always in a well protected nest and mother always came back.

Here are the pictures of the egg on day 8. Is it viable or am I wasting my time?

It could easily be viable, you would need to incubate it though. Ducks leave eggs in random places, not always where you would expect...

At 8 days, I would expect to see fine blood vessels through the "white" of the egg, possibly spreading out from an obvious center, but not necessarily. If you can't see any, the odds are the egg is not viable
See the picture here: https://permies.com/t/136969/Hatch-Long#1076336
I can try to get a better picture of the ones I've currently got in the incubator, but I don't really have the best camera for such a task.

Hatching it out may be a learning experience for you, but it's not really the best thing for the duck. It will be human imprinted for sure, and won't know how to behave among its kind. If it's a wild duck, there may be rules against keeping it as a pet, so you might want to check on local rules.

I try my best to at least get a Muscovy mom to hatch out duck/goose eggs for me rather than the incubator. I'm only using the incubator now as I believed I was having some sort of a fertility problem, and the incubator has confirmed this. I will keep the eggs developing, as I'm suspicious that I'll have a couple of moms that are currently on eggs, that may not have any success. This way, I'll tuck "ready to hatch" eggs under them and let them finish the job - at least that's the plan. Arguing with a Muscovy duck is often a loosing proposition, so I may get stuck with a problem, but at least they will be near adults from a very early age.