To fix this, add a new layer underneath the second piece or on top of the third piece. In the layer, draw shadow separating both pieces.
To fix the paper color that coming through behind the photo, we just need to simply reapply transformation process. Select the photo, hit Ctrl + T, use Warp if needed, and modify it until the color is covered.
Let’s take a look at the result. Our current result is using solid color as its background.
We can also add background by adding texture behind the torn photo.
As seen from the tutorial above, there are many ways to modify the final result. You can change the content of the torn photo, its photo paper color, and the background. The result below is using a portrait photo and I think it suits better because the photo subject is more recognizable.