How to checksum for a DVD under Panther?
It looks like Panther's hdiutil supports checksumming, even if the Disk Utility GUI might not:

hdiutil checksum myimage.dmg -type MD5


(The supported types of checksums are listed in the man page. A common one seems to be UDIF-CRC32. If you use UDIF-CRC32 or UDIF-MD5 the checksums will be calculated separately per partition.)

Or you could always simply use the md5 command:

md5 myimage.dmg