I have a good working method for merging photos perfectly. The first step after placing the photo is to decolorize the whole picture with a filter (Hue/Saturation > Saturation > 100%). Then I match the shadows/highlights to the original picture with tools like Levels and Brightness/Contrast. I hide the filter and I lighten the picture with another filter (Brightness/Contrast > Brightness > +80%). I match the colors to the colors of the environment (Color Balance and Hue/Saturation). After a few cuts, the placed photo looks part of the environment.
I will show the creation of the important parts in details. The first part was the temple on the left side; this was the most important one. I had the roof so I only had to search for resources for the columns. After I found two good pictures, I placed and matched them. Then I changed some parts to achieve a real 3D feeling (Fig.12). I thought the building looked bare so I decided to put a tree in the front of it. The building looked older now. After finishing it I created the steps and the pedestal (Fig.13).
I had to search for some photos to fill in the missing parts of the picture. Some new pictures gave me some new ideas. I used two photos to build up the stone arches (Fig.14).