It does seem legally rather dubious.
The concept is standard in many real estate deals.
Property titles often have limitations upon how the property can be
used, or how ownership shall change upon some event in the future.
Examples.....
- Life estates terminate upon one's death.
- Deed restrictions can require a single usage, eg, land donated for a park.
The concept can be applied to nude pix when they're shared with an
understanding that they're only appropriate in a particular relationship.
When it ends, it's reasonable that ownership of one's pix revert to one.
It would be good to have such an arrangement in writing beforehand.
But people lack foresight at the very time when such pix are taken.
So a legal framework to handle ambiguities is useful.