My son's photo vs a photo of my son
Solution 1:
My son's photo could mean 'a photo belonging to my son', but it will normally mean 'a photo of my son'. The context will in any case make it clear which is intended.
Solution 2:
my son's photo could mean
- a photo showing my son,
- a photo belonging to my son
- a photo taken by my son
or any combination of those meanings
a photo of my son can only mean
- a photo showing my son