I'm trying to mirror/clone a silverstripe website already installed. Right now everything works fine except the images/assets. I'm copying the File, HomePage, SiteTree tables&data from one database into the other so all of the relationships of the images on HomePage and File are exactly the same. However, these images don't show up in either the front or back-end... Am I missing something simple? I've also included the assets folder and all subfolders/files from the old to the new.

Any idea why these images aren't showing up in either the front-end or back end of the cloned site?

Have you tried throwing the site into Dev mode and manually doing some DataObject::get on 'File' and 'Image' to see what kind of error are thrown? Initially it seems like you have copied over the right DB tables and files to make this work.