Set a pick photo for a stack
The pick photo represents the stack. You can set the photo you like best as the pick, or Aperture can set the pick automatically. When you select and stack photos manually in the Browser, the leftmost photo becomes the pick. You can change the pick whenever you wish.
If the same stack appears in several albums, you can assign a different pick photo for the stack in each album. For example, a stack in a webpage album may have one pick photo, and the same stack in a book album may have a different pick photo adjusted for printing. An album pick appears with the Album Pick badge at the top of the image’s thumbnail in the Browser.
Set a photo as the stack pick
Do one of the following:
Select a photo in the stack, then choose Stacks > Pick, or press Command-Backslash ().
Drag the photo you want into the pick (or leftmost) position in the stack. When you see a green bar appear, release the mouse button.
Select an album pick for a stack that appears in multiple albums
Select a photo in the stack, then choose Stacks > Set Album Pick, or press Shift-Command-Backslash ().
To clear an album pick from a stack, choose Stacks > Clear Album Pick, or press Shift-Command-Backslash () again.