I use the following to seed linux distro torrents if I've deleted the original iso, but it can be used to just verify a good burn.
Unmount and copy the disk to a file.
Use "ls -l" to obtain the size of the original iso and the iso you just created. If they're the same size, great, use md5sum to verify the burn. But, if you notice the new iso is slightly larger than the original you'll need to shave off the end of the file before using md5sum on it.
sudo umount /dev/scd0
dd if=/dev/scd0 of=ubuntu.iso
This will create two new files xaa and xab. Use md5sum on xaa to verify the burn. (The xab file will be nothing but zeros. Use a hex editor to open it if you're curious.)
split -b ORIGINAL-ISO-SIZE ubuntu.iso