The PhotoDetailPage tag and it's children are used to describe how to create a larger view of a photo that the thumbnail from the index page is linked to. The size of the photo on the detail page is not specified in the template, it's left under the control of the user in the Create Web Pages Wizard. When designing a photo detail page, you have to keep in mind that the photo can be of any size.
The PhotoDetailPage tag has not attributes and does not have any text content.
A nice feature to note is that you can have multiple PhotoDetailPage tags. In such a case NeoPhoto will generate the first detail page using the first tag, the next one using the next. In this way you can have different PhotoDetailPages. The Comic Template has an example of this. If you click on a thumbnail and then click NEXT through the pages you'll notice that there are 4 different PhotoDetailPages.