Illuminate a new piece of typing paper and the photo (front, then back) at the same time.
Brighteners are used in most modern, post WW II, paper. Those will fluoresce a bright blue if hit with uv light. Old paper won't glow. If you walk around in the dark in a room with a desk, papers, books and such, some of that stuff will fluoresce and some won't. The paper that doesn't glow is most likely old.
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