I found this picture on a book cover. How can I duplicate the process using my image, in Photoshop.

Hi there

I used three images at random just to give you an idea how it could be done.

I selected the girl and inserted over the background scene.

I then added at the top of the pallet a third picture of a Christmas tree.

I grouped the tree layer to the girl layer below making a clipping mask that let the tree show thru. Using Layer> Create Clipping Mask

To limit where it shows I added a layer mask and used a foreground to transparent gradient on the mask to reveal the upper part of the girl.

Hope this helps

Butch