The "$1" in the right side of this rule refers to --"back-references"-- the part of the requested URL which matches the first parenthesized sub-pattern in the pattern on the left. In essence, it will "copy" that part of the originally requested URL into the new URL-path.
Unfortunately, you have no parentheses in your pattern, so therefore, $1 is undefined.
Also, you must use regular-expressions to construct patterns. Your "^CMSimg/*$" pattern will match a requested URL-path starting with "CMSimg" followed by zero or more consecutive slashes -- The "*" is a regular-expressions quantifier, not a wild-card as it is in DOS, for example. I'd suggest:
Based on these problems, I'd like to (kindly) suggest a thorough review of the documents cited in our Forum Charter [webmasterworld.com] -- Using mod_rewrite without a solid understanding is an invitation to disaster: Remember that each directive changes your server configuration, so this isn't to be taken lightly; One single character missing or out of place can cause your server to stop serving files, or perhaps even silently destroy the search ranking of your site over a couple of weeks...
[edited by: jdMorgan at 12:56 pm (utc) on Oct. 5, 2007]