Step 1 - Place two images in two different layers.
Step 2 - Add a Layer mask to each layer
Two images now sat next to each other, however they don't blend seamlessly yet as you can see the grey backgrounds are a slightly different shade.
To fix this, we need to create two Layer Masks, one on each layer, so we can apply a gradient that will make the two layers blend together. To add a Layer Mask, click on each Layer in the Layers Palette in-turn and click the icon which shows a circle sat inside a rectangle. When you do this, a white rectangle will appear in each of your layers this is a Layer Mask.
Step 3 - Apply Gradient
Click inside the white rectangle of one of the layers to activate the Layer Mask for the layer (we are going to start with the left portrait) then select the Gradient tool. Choose the background to transparent gradient. You can do this in the edit options that can be found in the top tool bar. Make sure the first Gradient option, Linear, is selected so when applied the gradient is straight and uniformed and keep the Mode on Normal and Opacity at 100%.
You may find it easier to hide the layer you're not working on so you can see the changes the gradient's made more easily. To hide a layer, just click on the eye icon in the layers palette next to the layer you want to 'switch off' and you'll no longer be able to see it.
Click and hold just outside to the right of the left photo and drag your mouse back towards it. You'll need to go over the left photo slightly to create the seamless blend we're looking for. Let go and you will see a gradient edge on the right side of the photo (notice how it's softer).
If it doesn't look quite right, or it's taken too much of your shot away, undo the last step and redo it, adjusting the start and position each time until you get it right.
Step 4 - Apply Second Gradient
Now we need to do the same to the right hand photo. If you hid the layer make it visible by clicking where the eye icon was and hide the other layer if you so wish.
Click and hold just outside to the left of the right hand photo and drag back towards the right to create a line. Let go and you will see a gradient edge on the left side of the photo. Again, if it doesn't look right, redo until it does.
Step 5 - Move the photos closer together
Now turn both layers back on and use the move tool to drag the right photo over the left until the blend looks right and you don’t see any of the transparancy underneath.
Step 6 - Crop and save
Use the crop tool to remove any excess canvas and save your image.