Except now I feel like an epic special snowflake. Am I being unreasonable? I don't expect my kid to be featured on the front page or anything, but to not even have a glimpse it feels as though he wasn't even there. As if he is excluded from the community. By the way, there are a dozen photos nearly all of which have multiple children in them, many feature multiple times. There are less than 12 kids in the room. I don't think any other kids were left out based on a quick headcount. (I just checked specifically to give you an idea of the context). It's a tiny thing in our lives and not something I'll lose sleep over, but wondering if I'm unreasonable to have mentioned it to them?
I think the bolded would be the issue if it were me in your shoes. I would worry that something had gone wrong with my child on that day that I wasn't being told about-that he was in a bad mood for some reason and avoiding the other children and activities, or maybe he was sick and not wanting to eat snacks with the other children, or any number of possible things, even little things, that would mean he hadn't been having a typical day (and was isolating himself, or had been isolated in a "time out" or such) and I think it would be very natural for a parent to worry about what might have caused that.
So, in my opinion, it might be going overboard if it were just about whether or not your child is in a picture every day, but to me it seems like the issue is more that multiple shots were taken of only a few kids total and your particular kid somehow didn't end up in even one of the shots. And I do agree that you shouldn't "lose any sleep" over it, especially if it only happens one day, but I also can see how you might get a bad feeling about something maybe being wrong.
If you are worried about what the day care people think of your inquiry, you might phrase it that way in a reply, that you just were worried that your child was not in any pictures because he wasn't interacting with the group for some reason and as a parent, your buttons just got pushed to think that maybe he was upset and hiding in a corner or something, even though that is a bit irrational.