I am not sure how critical this is now. If you search the forum, you'd notice that USCIS was issuing a lot of RFEs in 2005 for digital pics but lately there hasnt been any. I'd doubt that all the applications that they are receiving have non-digital photographs accompanying them. Its just that back in 2005, the pic quality of sub-standard cameras wasn't good enough to match a conventional photographs. well that would be true even today but number of sub-standard cameras has gone down, implying that most digital photographs shot at a photo lab would conform to USCIS standards.