This script and associated output shows what you see when using the validate option to check that a single-file backup was not corrupted as it was transferred from place to place.

validate Script

#! /bin/ksh

# Demonstrate and test the 'validate' subcommand of mysqlbackup,
# which works in combination with single-file backup.

bdir=$(pwd)/backup
full=$(pwd)/backup/single
image=backup.image
block=1234 # Arbitrary block to be corrupted

db564=~/sandboxes/msb_5_6_4
config=$db564/my.sandbox.cnf

mkdir -p $bdir
rm -rf $full
mkdir -p $full

# --backup-dir needed here for temporary work files while producing the single-file backup image.
# --backup-image could be a basic file name or the full path, it'll go under the same directory either way.
mysqlbackup --defaults-file=$config --backup-dir=$full --backup-image=$full/$image backup-to-image

echo; echo "*** Image File for Single-File Backup ***"; echo

ls -l $full

echo; echo "*** We expect this validation operation to succeed ***"; echo

# For validating, we need the fully-qualified filename, --backup-dir doesn't help.
mysqlbackup --backup-image=$full/$image validate

echo; echo "*** Producing corrupted copy of single-image file ***"; echo

dd of=$full/$image bs=8192 conv=notrunc count=1 oseek=$block if=/dev/random

echo; echo "*** We expect this validation operation to fail ***"; echo

mysqlbackup --backup-image=$full/$image validate

Output

$ validate
MySQL Enterprise Backup version 3.7.0 [2011/12/07] 
Copyright (c) 2003, 2011, Oracle and/or its affiliates. All Rights Reserved.

INFO: Starting with following command line ...
 mysqlbackup 
        --defaults-file=/Users/cirrus/sandboxes/msb_5_6_4/my.sandbox.cnf 
        --backup-dir=/Users/cirrus/downloads/meb37/test/backup/single 
        --backup-image=/Users/cirrus/downloads/meb37/test/backup/single/backup.image 
        backup-to-image 

INFO: Got some server configuration information from running server.

IMPORTANT: Please check that mysqlbackup run completes successfully.
            At the end of a successful 'backup-to-image' run mysqlbackup
            prints "mysqlbackup completed OK!".

--------------------------------------------------------------------
                       Server Repository Options:
--------------------------------------------------------------------
  datadir                          =  /Users/cirrus/sandboxes/msb_5_6_4/data/
  innodb_data_home_dir             =  
  innodb_data_file_path            =  ibdata1:10M:autoextend
  innodb_log_group_home_dir        =  /Users/cirrus/sandboxes/msb_5_6_4/data/
  innodb_log_files_in_group        =  2
  innodb_log_file_size             =  5242880

--------------------------------------------------------------------
                       Backup Config Options:
--------------------------------------------------------------------
  datadir                          =  /Users/cirrus/downloads/meb37/test/backup/single/datadir
  innodb_data_home_dir             =  /Users/cirrus/downloads/meb37/test/backup/single/datadir
  innodb_data_file_path            =  ibdata1:10M:autoextend
  innodb_log_group_home_dir        =  /Users/cirrus/downloads/meb37/test/backup/single/datadir
  innodb_log_files_in_group        =  2
  innodb_log_file_size             =  5242880

Backup Image Path= /Users/cirrus/downloads/meb37/test/backup/single/backup.image
 mysqlbackup: INFO: Unique generated backup id for this is 13234786599252660 
 mysqlbackup: INFO: System tablespace file format is Antelope.
 mysqlbackup: INFO: Found checkpoint at lsn 183521501.
 mysqlbackup: INFO: Starting log scan from lsn 183521280.
111209 16:57:39 mysqlbackup: INFO: Copying log...
111209 16:57:40 mysqlbackup: INFO: Log copied, lsn 183521501.
          We wait 1 second before starting copying the data files...
111209 16:57:41 mysqlbackup: INFO: Copying /Users/cirrus/sandboxes/msb_5_6_4/data/ibdata1 (Antelope file format).
111209 16:57:47 mysqlbackup: INFO: Copying /Users/cirrus/sandboxes/msb_5_6_4/data/test/innodb_busy.ibd (Antelope file format).
111209 16:57:47 mysqlbackup: INFO: Copying /Users/cirrus/sandboxes/msb_5_6_4/data/test/innodb_quiet.ibd (Antelope file format).
 mysqlbackup: INFO: Preparing to lock tables: Connected to mysqld server.
111209 16:57:47 mysqlbackup: INFO: Starting to lock all the tables....
111209 16:57:47 mysqlbackup: INFO: All tables are locked and flushed to disk
 mysqlbackup: INFO: Opening backup source directory '/Users/cirrus/sandboxes/msb_5_6_4/data/'
111209 16:57:47 mysqlbackup: INFO: Starting to backup all files in subdirectories of '/Users/cirrus/sandboxes/msb_5_6_4/data/'
 mysqlbackup: INFO: Backing up the database directory 'mysql'
 mysqlbackup: INFO: Backing up the database directory 'performance_schema'
 mysqlbackup: INFO: Backing up the database directory 'test'
 mysqlbackup: INFO: Copying innodb data and logs during final stage ...
 mysqlbackup: INFO: A copied database page was modified at 183521501.
          (This is the highest lsn found on page)
          Scanned log up to lsn 183524641.
          Was able to parse the log up to lsn 183524641.
          Maximum page number for a log record 467
111209 16:57:47 mysqlbackup: INFO: All tables unlocked
 mysqlbackup: INFO: All MySQL tables were locked for 0.000 seconds
111209 16:57:48 mysqlbackup: INFO: Full backup completed!
 mysqlbackup: WARNING: backup-image already closed
 mysqlbackup: INFO: Backup image created successfully.:
           Image Path: '/Users/cirrus/downloads/meb37/test/backup/single/backup.image'

-------------------------------------------------------------
   Parameters Summary         
-------------------------------------------------------------
   Start LSN                  : 183521280
   End LSN                    : 183524641
-------------------------------------------------------------

mysqlbackup completed OK!

*** Image File for Single-File Backup ***

total 237272
-rw-r--r--  1 cirrus  staff        188 Dec  9 16:57 backup-my.cnf
-rw-r--r--  1 cirrus  staff  121478567 Dec  9 16:57 backup.image
drwx------  3 cirrus  staff        102 Dec  9 16:57 datadir
drwx------  6 cirrus  staff        204 Dec  9 16:57 meta

*** We expect this validation operation to succeed ***

MySQL Enterprise Backup version 3.7.0 [2011/12/07] 
Copyright (c) 2003, 2011, Oracle and/or its affiliates. All Rights Reserved.

INFO: Starting with following command line ...
 mysqlbackup 
        --backup-image=/Users/cirrus/downloads/meb37/test/backup/single/backup.image 
        validate 

IMPORTANT: Please check that mysqlbackup run completes successfully.
            At the end of a successful 'validate' run mysqlbackup
            prints "mysqlbackup completed OK!".

 mysqlbackup: INFO: Validating image ... /Users/cirrus/downloads/meb37/test/backup/single/backup.image
 mysqlbackup: INFO: Backup Image MEB version string: 3.7.0 [2011/12/07]
 mysqlbackup: INFO:   Total files as specified in image: 188
 mysqlbackup: INFO:  Backup Image validation successful. 
mysqlbackup completed OK!

*** Producing corrupted copy of single-image file ***

1+0 records in
1+0 records out
8192 bytes transferred in 0.000953 secs (8596382 bytes/sec)

*** We expect this validation operation to fail ***

MySQL Enterprise Backup version 3.7.0 [2011/12/07] 
Copyright (c) 2003, 2011, Oracle and/or its affiliates. All Rights Reserved.

INFO: Starting with following command line ...
 mysqlbackup 
        --backup-image=/Users/cirrus/downloads/meb37/test/backup/single/backup.image 
        validate 

IMPORTANT: Please check that mysqlbackup run completes successfully.
            At the end of a successful 'validate' run mysqlbackup
            prints "mysqlbackup completed OK!".

 mysqlbackup: INFO: Validating image ... /Users/cirrus/downloads/meb37/test/backup/single/backup.image
 mysqlbackup: INFO: Backup Image MEB version string: 3.7.0 [2011/12/07]
 mysqlbackup: ERROR: Component file checksum mismatch found!.
 File path: datadir/ibdata1.$_append_$.2 
 mysqlbackup: ERROR: Backup image validation failed.