Define old. Are they seriously old, antique studio photos mounted on cardboard or mid-70's Polaroids or just some turn-of-the-century drugstore prints?



Depending on the emulsion, stock, degree of stuckness (?), value of the photos, etc, there will be choices. Back in the darkroom days, I had some luck with soaking stacks in purified water. Eventually they would let go and I could re-dry them in the open or roll them onto a drying plate for glossies.



A lot depends on the paper stock and how stuck they are.

I am thinking that this is something that WD-40 is not going to fix.