Yes, is there any precision in your contract ?
The legislation here is NOT closed, wich mean that even so, you might have good chance to own the rights in the last instance,
BUT (and it is a biiigggg but (or butt)), it means starting legal procedure...
If you really do not need these pics: for peace of mind, not loosing time and energy I would simply remove them.
end of the problem.
If not, maybe a agreement, depending how is the relation.
If a lot of money could be involved then you may consider the legal procedure as an option, but with no security.
Cheers,
Fred.