A decades old photograph - What is it we remember when all details are forgot?

A Photo of Mum, found in a box marked 'to keep'

Soft sunlight reflects her face fixed with pleasure, 
arranged by Dad, snapped with minimum fuss.
Frail yellowed paper holds her, captured,
enraptured, in a permanent maternal pose.
I place a kiss on her head and return her to the box
but hold the image a while, a reminder of a time now lost.
A memory, an image-blanket for my sleep, 
held close at heart, marked precious; one to keep.