You always have the ability to use the eraser tool to blend photos, but that can lead to blotchy results. You can also use masking, but there are also an easier method that doesn't require so many steps. First we need two photos to blend together.

Here is my first image.

Take your second image, and past it into your canvas. Here is the image I used.

Click on the second image you pasted, and choose Commands > Creative >Fade Image.

Depending on how you want your image to fade you can choose one of the eight fade presets. The preview image will give you an idea of what the result will look like.

Click ok and you will see that the corresponding portion of your second photo has been reduced to transparency, revealing the image below. Here is how mine turned out.