Is there a way to manually purge pictures taken by cellphone?

Normally you can use smartphone, open -> camera -> pictures and show them, then take them, so they are in your personal inventory.
Now sell them and they are gone.

Or do you mean all pictures from all sims in town?
You can check under cityhall -> MC -> town -> object stats -> inventory
Mark all photographs and accept, then accept all, this will delete everything.