The photograph that surprises you has interrupted an image memory had been maintaining.

Memory keeps editing without telling you. Faces get smoothed, rooms get rearranged, and the picture you hold of a person or a place drifts quietly towards what you expect, until a photograph turns up and disagrees. The surprise is the gap between the record and the version you had been carrying. Neither is a lie, though only one of them is fixed.

When an old picture unsettles you, look at it for longer rather than putting it away. Ask what your memory had altered and why that version was easier to hold. Photographs are useful precisely because they will not adjust to suit you.