Apart from the (small) possibility of post delays there is the (much bigger) possibility that your doco will be rejected. Mrs pineapple managed to have two successive passport photos rejected and got lucky with the third
As someone who owns and runs a photo lab, I can tell you that the quality of the photo, as well as dimensions, shadow (none), resolution and lighting are all more complicated than just standing in front of a 3mp camera and getting a photo taken.
We are listed for Australian, UK, Dutch, Greek, USA, Canada, India and lots more, and if you think all the photos are the same, you are totally wrong.
In 2 years we have only had one rejected photo, and that rejection was reversed after I "discussed" it with the post office owner at the time.
Photo booths in shopping centers are no longer capable of giving the required quality for a biometric passport photo - your local camera shop/photo lab should be able to do it for you, and generally in a more professional format than a chemist with an instant print kiosk.
You may or may not know (or care) but the whole passport photo specs were designed by the DSTO at Edinburgh in South Australia, and those specs have been taken internationally. There are official requirements for camera resolution, lens focal length, printing resolution, background, head height, type of paper it is printed on and a lot more.
And most importantly, they are NOT a fashion statement any more.