iPhoto '11: selecting photos
To select a photo, click it. A selected photo has a yellow border.

Here are other ways to select photos:
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To select more than one photo, hold down the Command key while you click each photo.
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Drag to select multiple photos.
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To select a continuous range of photos, click the first photo, then press the Shift key while you click the last photo.
Note: You can use these same methods to select one or more Events or Faces snapshots.
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