Selecting a photo to print, choosing Page Setup, and changing the scale percentage does not affect the printout. It still prints full page.
This happens when using:
iPhoto does not use Page Setup scale percentage as a means of scaling printouts.
To achieve different single page print sizes, do the following:
1. From the File menu, choose Print.

2. From the Presets pop-up menu, choose Standard.
3. From the Style pop-up menu, choose Standard Prints.
4. Select the size of the printout using Size.

Other page setup values besides scale are used. It is important to select the correct printer type and paper size within page setup for best results when printing.
Note: If you select Preview from the Print dialog, the selected photo opens in Acrobat Reader or Preview where you can change the scale percentage in Page Setup.