The rules with MLS are the same as those for copywriting. They don't belong to the owner, unless the owner took them or paid for them. They may not belong to the agent, if the person they hired retained their rights to the pics.
New pics are for a new season anyway! New pics can often create a new view of your property.
The photos belong to whoever took or provided them. There could be copyright laws protecting the use of them.
If you took the photos, then there is no problem using them again. MLS does not have any rules preventing the reuse of photos. The copyright issue comes up if the photos belong to the agent that originally listed your home, and then you hire a different agent when you relist it. That agent cannot use the previous agents photos. Besides being unethical, it's just plain lazy.
Armstrong Field Real Estate