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How do I synch photos onto my iPod nano without replacing all of the existing photos? - photos of ankylosing spondylitis in dogs

I have a new laptop and want to transfer more photos on my iPod too. If you click on the pictures on my iPod, while I clicked synch photos. When you click Apply, displays a message that with another library or folder is synchronized. He said it would all other photos with the folder that you selected to replace it. Is there a way to load more photos to my iPod without having to replace my old one?