We will be referring to the images used in this tutorial as waterfall and stream.
Use the move tool to drag and drop one picture and place it on top of the second picture. I moved the waterfall on top of the stream.
In the Layers window click on the top layer to select it and then Go Layer, Layer Mask – Reveal All.
Once the vector mask is added (and with the layer still selected), select the gradient tool (Under the Paint bucket tool in the toolbar).
Drag the gradient point from bottom right to top left. Once you release the two images will be blended together.
The length of dragging depends on the visibility of each picture that you wish to achieve. You can keep on testing out different dragging until you are happy.
You can also try out our other blending tutorial, How to blend images in Photoshop - Method 1