Each "virtual host" in the Apache environment is described by a series of directives, in this case particularly including Alias, ScriptAlias, and Directory. These directives tell Apache what to do with each URI.

If you are using mod_rewrite, these rules are applied to the rewritten URI.

In this case, you want certain aliases such as images/blah to simply be served from a certain existing disk-directory. The Alias directive can do that. (If you're using mod_rewrite, the rules must also allow these URIs to pass-through unchanged.) For these aliases, Apache is just doing what Apache normally does:   scooping-up the content of a file and shoving it down the pipe. The browser's also doing what it does best, caching things and not asking for them a second time unless it thinks it has to.

You control what actually gets sent to (Perl), and this should be:   only the content that truly must be generated by a (Perl) program.

What you are shooting-for is definitely a good thing, by-the-way. Let Apache do what it already knows how to do best, whenever possible. Bring Perl into the picture only for things that require a programmed response. Use custom error-documents to keep the overall site look-and-feel consistent while still letting Apache itself do a portion of the “heavy lifting.” Be aware of the natural caching behavior of browsers, also, and make sure that this too is working to your advantage as designed.