Hi C.,
It is really easy to get a photo. Most photo places know what is required for a passport - color of background, size and which angle is needed.
I got ours done at Wolf Camera and Video for $16 I think.
The other posts say Costco is less expensive, but if you do not have a membership - Wolf is another place.
I would avoid the passport booths - kids won't stay still for the perfect photo!
The only thing with a baby photo is that they must have their eyes open. (My daughter was 10 weeks old when we needed hers - so this took a bit of doing to be satisfactory).
A child passport is only for 5 years, not 10 as for adults.
We filled out the forms ahead of time (which we picked up from our local post office which had a passport office attached).
It is usually a "come in and sit and wait and take a number system", so take lots of toys and things to keep little one occupied. (There is usually no bathroom - but sometimes the staff will feel sorry for you...)
Saturdays are the busiest day, but if you go early - you are better off. Weekdays are less busy, but both parents need to be present or else you need a special letter as it states in the form. Passport offices are usually open 9-3 but check for local variations (and days!).
Make sure you take 2 checks - one for the passport office and one for the Post Office.
The waiting at the office is the hardest part.
Apply now for the summer and you can avoid the summer rush and be sure to get your passport before travel time. You can expedite it in a number of ways but you pay a lot extra.
I applied in June for travel plans in August and had to expedite to be sure to get it in time. (Was trying to fit a trip in to my family while on maternity leave - so timing was a crunch).
They usually have it posted up at the office how long passports are taking. Whenever it has said 4-6 weeks, I have always been surprised when it comes back in 2-3 - even when I have not been expediting.
Hope this helps!