All of the photos from your Classic website will remain there after you transition to Clover Sites (even if you've copied this content for your new website).
Step 1 - From your new Greenhouse, click on any photo section to receive the message below
Step 2 - Click the Yes, Import My Photo Album button to automatically copy your previous photos to your new website
It may take a few minutes for all of your photos to show up. You may also need to refresh your Greenhouse for the photos to appear.