Thought of sharing the following tidbits of wisdom gleaned from Passport Canada (IRCC office) photo studio in Scarborough (we visited this place as a result of photo requests for our kids)-
a. DON'T wear white shirts or dresses, particularly covering the shoulders- made my younger kid put on a sweater for his picture to be taken.
b. Ensure that the photograph they take sits within the circle- these guys here had some software that prints the picture inside this 'reference guide for photographers'
c. There is a particular way in mailing these photos which they have requested. 1. Ensure to send the original photo request letter they sent through. 2. Put the 'reference guide' letter which has your photograph printed as per the specifications (Point #2) 3. Get a photocopy of the mailing receipt and place one inside the envelope(s)- there have been multiple cases reported where IRCC states it wasn't in the timeline of 30 days. 4. Send the required photographs,as appropriate.
Hope this helps.