It's really hard to tell from photos, particularly photos of horses that 'we' aren't at all familiar with. I have one mare here that, when she was carrying a foal every year, was absolutely huge in the belly. If I had posted a photo of her right after she foaled, or any time in the months after she foaled, everyone on this board would have said she was in foal, surely due any day! She had 2 or 3 foals for us & then we left her open--and all the following year people would have said the same thing if they'd seen a current photo--definitely in foal! Now that she's been left open for several years, her belly has gone away and no one would take her to be in foal in current photos.
Some mares can look like they aren't in foal when they actually are; others look like they are when they aren't. If it's a horse "we" know, we can often tell that the mare is or isn't in foal. A horse we're totally unfamiliar with--it's really just a guess. Just because a horse looks "exactly" like like a horse we know personally, that doesn't mean that other horse is truly in foal just because she looks like that other horse that we know to be in foal.
That said, in looking at your photos I would say the first two probably aren't in foal, or if they are, they won't be due for a long time yet. The 3rd one could be--but I wouldn't say she is very close. Of course it's rather a guess just how much is hair and how much is horse--worse in photos than in real life because we can only see and not feel through the hair. One of my mares once looked to be very much in foal, which should have been impossible, but once I clipped her belly she quite obviously wasn't in foal....it had all been hair.
As for why some people pasture breed--often they have better conception rates. Or it can be that the mares are pastured for the summer and, especially if there are a number of mares and/or it's a large pasture--it's so much easier to put the stallion out. It can be a lot of work to go out & catch each mare to check her & then breed her. Quite honestly, there are people whose mares are pasture bred and those people still know the breeding dates for each mare, and therefore they know when the foals are due--it's just a matter of paying attention to the horses, and taking note each day which mares the stallion is interested in, and which ones he's covering. Likewise there are some who hand breed but never keep track of anything at all, then by the next spring they can't remember when they bred each mare.
