This note is based on the suggestions at MacRumors.

There are possibly better ways to do this, but here is one way to print US passport size photographs from your Mac, assuming you have what I have:

• MacBook running Leopard (though the model/OS version are obviously not hard requirements)
• iSight or a digital camera
• iPhoto or similar image editing software
• Keynote (Apple’s equivalent of MS Powerpoint)

I am using Keynote to scale the image down to 2″ x 2″ and print it. If you do not have Keynote, you can probably use other editing software such as ImageWell — anything that lets you display rulers in inches.

First read the instructions at the US State Department website. Here you will find critical information on size of the image, background, lighting, photo print quality and other requirements.

Step 1
Take a photograph using iSight or (better) a digital camera and add the picture to iPhoto. Then use iPhoto’s built-in editing capabilities to crop the image, constraining it to a square, until the image details meet the requirements at the US State Dept website (link above).
Step 2
Start up Keynote and create a slide using a blank template. Choose View -> Show Rulers to enable rulers and then, in Preferences -> Rulers, set Ruler Units to Inches.
Step 3
Click on the Inspector and in the Document Inspector tab, set the slide size to something smaller than 1024×768, say 800×600. Now, back in the main window, make sure that the new slide size is less than or equal to 8.5×11 inches — the standard print size in the US and quite probably the size of the paper in your printer. If you are going to print on a smaller photo sheet, choose an appropriately small slide size. The idea here is to prevent Keynote from scaling the slide (and hence the image(s)) down to fit on your printer page.
Step 4
Copy paste or drag-drop your photograph from iPhoto into the slide. Use the resize handles and with the rulers (or the resize balloon info) as your guide, resize the photograph to 2″ x 2″. Make additional copies of the resized picture on the same slide, if you need more than one passport sized photograph.
Step 5
Set your print preference to a sufficiently high resolution (dpi), turn off border printing and scaling in Keynote print options, and print away!
Update

EPassportPhoto is a website that will do a lot of this heavy lifting for you (discovered via a friend’s blog).