Is it possible to see disk usage of pictures, videos, music, etc.?
Under iOS apps are allowed to access only their private storage and cannot access any other files on the disk. For this reason it isn't possible to go through all the files on the disk and determine their type.
Disk consumption of individual file types could only be provided by iOS but this isn't the case right now.
However, it is possible to see the sizes of the installed apps using iOS Settings - see