Ah, I see what you mean now... you want your client to have LIMITED ftp access so they don't fool about with core files!

You may be able to do something in your host C-Panel - see what options are available for public ftp settings. As this is essentially not a zencart issue, you may have to contact your host to discuss solutions. A custom script may be needed to have the images "copied" to another directory - or perhaps even to your client's hard drive...