iPhoto's next toolthe cropping toolrequires that you select a portion of the picture first.
To select part of a photo:
In edit mode, drag to create a selection rectangle in the image. iPhoto fogs the photo outside your selection rectangle to help you focus on what you have selected (Figure 4.17).
Figure 4.17. To select a portion of a photo, drag to create a selection rectangle. Move it by dragging it; resize it by dragging an edge. Here I've created a selection rectangle with no specific proportion to focus on the seaplane and the odd truck.
To move your selection rectangle around, drag it (your pointer should be a hand). You may need to move a selection rectangle to align it to the edges of a picture, since it's hard to start selecting right at the edge.
To resize a selection rectangle, drag the rectangle's edge.
To constrain the selection rectangle to specific proportions, choose an aspect ratio from the Constrain pop-up menu. If you haven't created a selection rectangle, it will be constrained when you do; if you have one already, iPhoto resizes it (Figure 4.18). To remove a constraint, choose None from the Constrain menu.
Figure 4.18. To constrain an image to specific proportions, choose an aspect ratio from the Constrain pop-up menu (here I've chosen 4 x 6, which will make a good print while not detracting from the subject of the picture). You can move and resize the selection rectangle while maintaining the selected aspect ratio.
To constrain the selection rectangle to custom proportions, edit the image in its own window, and enter the desired aspect ratio before you start selecting.
To deselect everything and start over, click in the fogged area.