how about
tar -cf test.tar someDir | md5
&& rm test.tar???
the blue part creates a "tarball" (Tape ARchive) of the directory "SomeDir" and all its files and subdirectories recursively, and the gray part is an optional part to delete the tar file after you've run an md5 checksum on it.
If disk space is an issue while creating the temporary tarball, modify the command to read
tar -czf test.tgz someDir | md5
&& rm test.tgz instead. This will create a compressed tarball to run the checksum against, and, as before, optionally delete the zipped tarball after the md5 has been run on it. This second way takes a bit longer to execute, though, but disk space savings during the lifetime of the tarball can be quite significant. You won't gain anything, disk space savings-wise, with ".mov" files or ".gpg" files but you sure will with text-type files, like .doc, or .txt or .rtf.