A common problem when photograhing groups of people is that some people are not availble for the group shot. Useing photoshop layers, masking and blending, people can esily be added. This series of photographs shows the results of this process.
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Here is the typical group image. In tyhis case, we are missing two people:

Here a separate image of the two missing people, taken later. Note the lighting and the size of the people is different than the first group image:

Here's the final composite:
And here's the same merged image but showing where the two added people are (in case you can't easily locate them):

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