The photo's usually aren't a problem for the london office but if they're not up to spec there will be a problem with producing your PR card after landing.......as i have found out
12 weeks after I landed I got a letter through telling me the photo submitted (which is attached to your COPR by london office when you submit your passport) wasn't up to spec so I had 30 days from the date of the letter to send in 2 new photo's up to spec. It's been 16 weeks now since I landed and still no PR card! I'm told it takes 6-8 weeks from re submission of photo's.
If you are dropping off your passport it's probably worth a stop at charing cross. There is a photo place called ID photo (I think thats the name) i've since found out they have great success with being accepted by the equipment that produces our PR cards.