Here’s my Photoshop file if it might help you make your own.
Guidelines for U.S. Passport photos are here and they provide a photo template for an example.
So what worked for me was to align the example photo they provided into a 600×600 pixel square in Photoshop.
Here is that Photoshop file with the guide photo already in there.
What I did is paste my photo on top of the example, then change the opacity to 50% so the guide shows through, then use Free Transform to make it the perfect size and alignment to match the example. Then raise the opacity back to 100%.
Here’s a random portrait snagged from MS Clipart, which is not a good passport photo – not plain white background, not looking at the camera – see, I’m getting good at this!
Next I made another Photoshop file at the right resolution to print at 4×6, with guides in place to help align the photos.
Select the whole square and copy, then paste it into the second Photoshop document with the guides. Here’s that second file
Three passport sized photos fit nicely on a 4×6″ which can then be exported and printed for seven cents at Walmart. That’s two for the passport office and one in case you make a mistake in cutting.