Article Updated Feb 2012.
Here we show you how to use Photoshop's layer mask so you can create an overlapping and smooth blend of two photos.
Step 1 - Open the two photos
Open your images up in Photoshop and adjust them so they sit side-by-side in different windows.
Step 2 - Extend the canvas of one of the photos
We are going to extend the canvas of the photo that's going to appear on the left to at least twice the size of the original image but before we do this, we are going to double-click on the layer in the layers pallette to turn it from a Background to a Layer.
When we do this a window will open where we can rename the layer and we are going to call ours 'left portrait'. With this done, we can now extend the canvas size. To do this go to Image>Canvas Size (Alt + Ctrl + C) and click inside the centre left Anchor square to make the canvas expand on the right (as the above image shows). Click Ok and your image will now have more space to the right of it.
Step 3 - Move the photos together
With the Move tool selected, click on the right hand photo and drag it over to the left hand photo.
Or, with the right photo's window active, go to Select>Select All, and then go to Edit>Copy. Then click on the left photo and go to Edit>Paste. Use the move tool so position the photos so they're sat side-by-side.
Both photos will now be in the same window and you will see the Layers Pallette now shows Layer 1 (the photo we dragged over) and left portrait (the shot we dragged the other on to). We are going to rename Layer 1 to make the tutorial easier to follow but you don't have to do this if you don't want to.
Step 4 - Add a Layer mask to each layer
Our two image are now sat next to each other, however the 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 5 - 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 chages 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 6 - 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 7 - 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 dont see any of the transparcny underneath.
Step 8 - Crop and save
Use the crop tool to remove any excess canvas and save your image.
Note: As you become more familiar with layers you can do the gradient mask with the layers in this overlapping state, and use the brushes to mask in a more complex way, extending some areas of picture one over picture two to give a far more precise blend. But this was just to give you the quick rough and ready basics of layer mask and image merge.