One thought is to contact the cruise lines and prove that this is your pic that was used without consent. From there you have a few options

1. They can continue to use but have to give credit by amending the painting to add your name
2. Go the lawyer route as others mention here
3. Do nothing
4. Shame them on social media

The last option may not do much because it may not be reach enough people to have an effect that solicits the cruise line to do anything.

The first option is the best imo because it is free advertising for you