In File Explorer, you will see a Libraries section. When you open it, there are predefined categories for Documents, Music, Pictures and Videos. Each Library, by default, includes your own folder and the public folder (EXAMPLE: C:\Users\Pallentx\Pictures, C:\Users\Public\Pictures)
You can add any folder on the computer (or network) to your Library and it will get indexed. For example, if you have a second hard drive that contains a lot of pictures, you can add D:\Pictures to the Pictures Library. When you open the library, pictures from your main picture folder and pictures from the external will all be gathered into the Library for you. The Photos app will also pull them in for viewing. If you don't want pictures to show up in the Pictures app tile, they need to reside in a folder that is not part of the Library. For example, if I make a folder C:\Users\Pallentx\Drawings and don't add that to the Pictures Library, the Photo app will not know that they exist on the computer.
I don't think there is a way to have pictures in the Photo app, but not show on the live tile. In that case, I would just turn off the live tile and let it just be a blank launch icon.