I see your point, I really do.
I can assure you though, that the problem isn't rooted in semantics, and here's why:
Yes, each individual has their own context in which to value things, people, ideas, etc...
... But it's possible for each person's valuation of something to be incorrect, even accounting for their specific context.
Here's an example:
"The free market, made up of individuals making decisions of value at the margin, is better than a system in which a centralized power controls markets/prices.
Why?
Because no single entity can possibly be omniscient enough to calculate every single price accurately enough to sustain an economy for long."
Okay, so in the above example (which myself and most Austrians use) implies objective value. It suggests a link between omniscience and knowledge of value. To be omniscient would be to have intimate knowledge of every person's subjective context. In addition, an omniscient actor would know what to value in each of those contexts. Again, this implies right and wrong answers with respect to what we ought to value.
I don't think I prefer free markets because they're good for me subjectively. I believe free markets are good because when making valuations I want to approximate objective reality, relative to my specific context, and valuing free markets seems to be objectivity better than valuing centralized price control.
Here's another example:
Regret.
One can look back on their decisions/actions (which are really just valuations because action implies value) and realize that what they did was wrong or sub-optimal.
I could strongly believe that walking up to my neighbour and punching him in the face is a good thing. That's a subjective valuation. But in most cases, punching one's neighbour in the face is not a good thing to do, and I would immediately regret the decision. The subjective valuation was wrong in this case.
So, in the case of valuing your child's photographs, I think you are correct that the photographs are only valuable to you and perhaps other family members, but I would argue that they are objectively valuable, relative to your individual context. It makes sense that you value them. It's possible that you'd be wrong not to value them.
All valuations are subjective, but that doesn't mean that answers to the question "what is valuable" are subjective. Does that make sense?