I"m able to see all WhatsApp photos and videos when I open gallery ('Photos' is the gallery name in 8.1). But I checked everywhere and couldn't find where those media files are located. I searched in WhatsApp folder and could see only folder named 'backup' there. I actually wanted to move some of the WhatsApp photos and videos from phone to computer.
Phone : Lumia 630 Os : Windows Phone 8.1
Addition : I just noticed, not just WhatsApp even the photos and videos are unavailable.