If you provide the photos to be edited, the rights to the photos remain yours. You own the rights to the editing work done on the photo by the freelancer as well, through a "Copyright Transfer" that occurs when you accept the work done. Additionally, you can get the freelancers to sign an NDA (Non Disclosure Agreement) before agreeing to work with them. The NDA ensures that the freelancer will not discuss or share the job details with third parties.