It might be the fault of what screen I'm using to see the photos, but I don't actually see veins in any of them. For the incubated eggs, I think i'm seeing an overall darker appearance (maybe thicker shells or darker brown shells, maybe something inside the eggs), and I see light spots where the shell is probably thinner.
If they are developing, and your light is bright enough, and the shell is not too dark, I might expect them to look like some of the images near the top of this page:
https://incubatorwarehouse.com/pages/egg-candling
I've seen similar things when I've tried candling eggs, but I've also had times when I couldn't see anything because my light wasn't bright enough. And I've had times when the light was bright enough but I could only see inside some of the eggs, because the others had shells that were too darkly colored. I've never tried taking pictures of eggs when candling. So when I don't see anything in pictures of candled eggs