The hardest part is getting the background shadow minimized. The State Dept has recommended a 3 flash system with two diagonal flashes in front, and one in the back pointed up just to remove any shadows. I took my kid’s photo outdoors, and with it being bright enough but without any direct sunlight I managed a photo with no background shadow,
The State Dept has that online tool, but it seems that it’s mostly for visa applications, where the photo can be electronically transmitted with the application. US passports still require a paper photo, but only one these days. For those posting from other countries, are there electronic photo uploads these days? I thought maybe the State Dept could do that, even with paper applications. They have an online application generator, which saves everything to a database. The paper copy is a formality, although I believe it needs to be signed. They have a matrix code to scan, which should bring up the application as submitted online. It should theoretically be possible to upload a photo to save to the database.