After Opening your images in photoshop, using move tool drag one image into the window of the other image
This will automatically create a new layer that contain both image in one document
Unlock background Layer simply by double clicking it, this will enable you to make changes in both images
Now you need to resize and position your image, click on a layer that you wish to resize/reposition and press CTRL+T, your image will have handles that will enable you to resize and reposition as you desire
When you are happy with the transformation simply click enter to accept the changes
Now we can start blending two images together, simply by adding a layer mask on Layer 1, hence simply make sure layer1 is selected then click on add layer mask icon. Layer mask thumbnail will appear beside layer 1
From tool palette Select gradient tool, make sure Layer mask is selected
Your settings should reflect below
Start blending images together by dragging the gradient tool from where you want the transition from on eimage to the other to begin, release your mouse once done
Now you can see the place where transition took place is faint hence simply take a eraser tool and paint over that area to enlight it
This is done, well now you can play with color,light and exposure as you desire
