Your still going to have to figure out how to do it. If you do not write a script then you are limited to what you can do by hand right.
So you would have to manipulate the data in some fashion to allow you to do what I outlined above.
You can import a photo into another photos table say with an id of 25 if a photo with 25 already exists. Same for categories.
So whatever manipulation you do would be extensive.
Like for instance. Say you want to shadow create 10 new categories to mimic the old site. Your best bet is to create those categories in your main sites edit categories because all directories would be created in the data folder and permissions set right. You would then if your manually using phpmyadmin to import photo entries you would update any cat ids to the new ids on your main site as well as change any userids to one that exists on the main site maybe yours. You would also need to redo the id fields on these entries to take into account using id fields that do not exist in your main sites photos table. Then you would move any images to the main site.
It is really best that you write some script to do what you want.