dd errors with certain DVDs

[Paul Smith]

On 3/27/07, Tony Nelson <tonynelson at georgeanelson.com> wrote:
> dd if=/dev/dvd bs=2048 count=$(isosize -d 2048 /dev/dvd) | sha1sum

Does the above work in the case of CDs? Can one correctly create an
iso of a CD with

dd if=/dev/dvd bs=2048 count=$(isosize -d 2048 /dev/dvd)

?

Paul