Replace with one comment and one line of code:
# Skip all following rules for /articles/images/ path requests
RewriteRule ^articles/images/ - [L]
Note that this rule as coded here and above excludes only the /articles/images subdirectory (and everything in it and below it) The directory "/articles" itself and the pages/files in it are not excluded. Make sure that's what you intended.
Remember to delete your browser cache before testing any new server-side code.
Warning: There is no such thing as a "404 redirect." It is either more-accurately termed a 404-error document rewrite, or you have a potentially-fatal error lurking in your ErrorDocument directives. Be very sure that your ErrorDocument directives refer to filepaths, and not to URLs. Getting this wrong is the simplest way to cripple a site in the search results.