If you’re ever confronted by someone who forces you to delete your photos (and our magical photographers’ rights gray card doesn’t work), go ahead and delete them! What most people don’t know is that deleted photos can easily be recovered afterward. Even photos on a memory card that’s formatted and completely wiped can usually be restored.
How to Recover Deleted Photos from a Memory Card with PhotoRec
http://www.petapixel.com/2010/10/13/how-to-recover-deleted-photos-from-a-memory-card-with-photorec/
Photographers Rights Gray Card Set
http://store.petapixel.com/products/Photographers-Rights-Gray-Card-Set.html
(15 dollars for the set)
In the USA a court order is required to force someone to delete images.
If they threaten you and tell you that deleting the images will prevent other even worse action by them then that is called "coercion" and this is illegal too.
you can also try recuva to recover your photos
http://www.piriform.com/recuva