I would say that a one-time occurrence of your child's picture not being there is not something to bring up. I'd notice it, and then keep an eye on the situation. If it happens again frequently, then I'd mention it.
The teachers are busy enough with the kids. Adding one more task to their day--making sure every child gets a picture in the newsletter--especially when that task is for the parents' comfort and not for the kids, is asking a lot. I'd rather have them interacting with the children, not counting heads in photos.
If you think there are on-going issues with your child not being treated fairly or well, then it is best to bring up those issues specifically. The lack of a photo on one day might be a sign of that, but it's a teeny, tiny thing. Not, IMO, enough to judge the teachers on.
If you are worried that you aren't getting the full picture, daily, about how your child is doing in the class, then ask directly. I think it's a bit of a stretch to think this on the basis of one missing picture in one newsletter.
And I have to say, from the outside looking in, this:
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.
does seem like an over-reaction. It was one day, out of many days. If your son is old enough, ask him where he was during the picture taking. He might be able to give you a fuller picture of his day.