The software that makes it really easy though. However, there really isn't that much difference between what a person can do at home these days, other than perhaps the quality of the camera. And you don't really need a dSLR for a decent passport photo.
I'm not quite sure why they would require a "professional". I've seen it done at certain places that would meet the "professional" requirements, such as a warehouse store or pharmacy, and often it was just an inexpensive digital camera. The real key these days is cropping/formatting it properly. I think I could teach my 7 year old to do it in a few minutes. The requirement for a "professional" sounds more or less outdated.
As for my case, I picked up the photos today at Target. They were just kind of sitting there on a rack at the machine. I'd gotten a message early this morning saying they were ready. Target says they use an RA-4 wet process, but I think these days most of these machines can't be used to process color film. They seem to be only for making digital prints. I kind of pointed it out to the clerk, who looked at it and said she hadn't seen anything like it before. I paid for three 4"x6" sheets, but it came with an invoice, as well as one ad sheet for passport photos done at Target. It said $12.99 and showed an example of what it would look like, which was two photos printed to a 4"x6" sheet of photo paper.