Photoshop - Creating a Montage (Combining Photos)
1) Open your first image. Then place the second image above the first one.
2) Click the Add Layer Mask button at the bottom of the Layers palette.
3) Select the Paintbrush Tool from the tool bar, select a large brush
4) Click on the Layer Mask thumbnail, and slowly paint around the contour of baby layer.
5) Then place the 3rd image and repeat the steps 2-4.