Backing up with rsync, how not to get into trouble with permissions and privileges? I am backing up files to an external hard drive using rsync as a test, usually I just copy pasted but I read that rsync is more reliable and does a checksum to verify the copy so I am trying it out now.

I'm just using it as: rsync -a --progress [SOURCE] [DESTINATION]

I noticed in the manual page relating to rsync that it also copies the permissions and privileges, in fact after the copy when I right click and "get info" on the files and folders, they have the same "Sharing and Permissions".

When I check files backed up during previous backup processes (using copy/paste), sometimes the permissions are "read &amp; write" for the current user (me) and "no access" for everyone else, some have "read only" for everyone and spotlight.

My question is: how can I be sure that the backed up files and folders will at least be readable by future users on my external hard drive. In other words, when I'll access the hard drive using a fresh clean install of my OS using a new/fresh/possibly-new-with-a-different-user-name-account, how can I be sure that I won't be locked out of my files by permissions etc ? I would like to at least get read only. 
Do I have to manually right click every file and folder then "get info"  and go to "Sharing and Permissions" and then choosing "Read &amp; Write" for everyone ?

Thanks !
You can always access the files by being an admin on the computer you attached the external drive to and changing them. The admin super-user can always fix permissions issues.
You can change permissions at the top level by clicking "Apply to Enclosed Items" That will change everything in the folder and below.