You have two or more images that you'd like to combine. How do you do it? In this tutorial I will share one way to achieve this task.

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Open the portrait that you wish to merge.

Duplicate the portrait layer

 Open the background that you wish to merge with the portrait

 Move the portrait layer higher in the layer list than the background

 Select the portrait layer

 Click the magic wand tool and select the black background, then invert the selection (Image>Adjustments>Invert)

 Next copy your selection (Edit>Copy) and Paste it (Edit>Paste) which will paste a new layer that doesn't have the black backgroiund.

 To see the changes you will need to hide (click the eye icon to the left of the layer name)  

The result: