Just thought I'd add my experiences with new photo requests. About two months after landing, I got a message in my CIC account stating that my photos (taken at a local Walgreens in Boston) had been rejected, and I needed to send two new ones within 30 days. The reasons for rejection were not given.
After consulting with a local photographer who specialized in Canadian photos (Albert's photo studio in Waltham, MA), I found out that I made the mistake of wearing a white shirt (with light blue stripes) in the photo. These tend to blend with the white background and usually get rejected. So I took a new photograph at that new location with a back jacket on. The person guaranteed that it would work this time, as she had done hundreds of photos for Canadian PR card and passports (and it worked!!!!).
My second concern was, would CIC accept photos mailed from outside Canada, i.e. Boston? Would they have an issue mailing it to a Canadian address while I was away? Only one way to find out => I mailed it directly from my US address. Turns out they couldn't care any less about where the new photos are mailed from.
My third concern, would my PR card application be pushed back to the end of the wait list, i.e. another 60 days of waiting? No. The new photos were processed about 2 weeks after their receipt and my PR card was mailed within a month after the request.
Hope this helps clarify some concerns.