We live in a so called 'posh, middle class area' where the majority of families at my ds's school have plenty of money etc. There are however a number of less advantaged families who have children at the school, mine included. Some have been moved into local housing by the council or housing associations, but they are no better off financially and still struggle to make ends meet, my own situation is more complicated and although we live in a good area, we also struggle financially.
School jumpers and cardigans with logos on are compulsory (it is in our home-school agreement) only supplied by the school office and are £12 per jumper. I cannot afford to replace a jumper every time one of them marks theirs with whiteboard pen (which is regular occurrence).
I used to keep a spare one for each of them just for school trips and photographs, but I can no longer afford to have a jumper each sitting in the wardrobe, only getting worn three times in a year before its outgrown.
My children are always correctly kitted out for school, quite apart from anything else, I was bullied myself at school for not having the same uniform as everyone else and never want my own children to go through that, but far from looking smart, particularly by this time of year, their jumpers are worn, washed out and I suppose pretty scruffy (by my standards anyway). I simply can't afford to replace them, when they will most likely be outgrown before September. Not to mention that come September, all the other children have nice bright new uniforms to wear and not having the same would mark my boys out as difference or 'less than' in an instant.
Now apparently I have to worry that some teachers and parents will consider my children potential trouble makers just because we don't have the money to keep them in brand spanking new unforms for the whole of the school year. Nice. 
I also think its awful that anyone thinks a school photo is ruined because the child isn't wearing a jumper with the school logo on. Surely the point of the photo is a memento of the school year for the child and a memory of their child at that age for the parents - absolutely nothing to do with representing the school. My children's jumpers may be a little worn, but they still look lovely in their photographs and I am proud of them whatever they wear.
To be honest, if the school did something about the daft photographer that insists on taking pictures of the children in silly poses, and over contrived positions, their school photos would be vastly improved regardless of what they are wearing.