FTP uploaded images not displaying

I am currently a Dreamhost customer using WordPress on several sites, and it appears that a new site of mine – the first I’m building for a client instead of just myself – has an odd problem I’ve never seen before.

For some reason I can’t quite figure out, no plugin or page can link to an image that I upload into a directory on the server with an FTP client. I’ve set permissions, tested direct image calls – I can get them just fine by typing the direct URL into my browser – but my site just can’t or won’t display them.

One thing in particular that this has broken is the AdServe plugin, which now cannot display the edit/remove icons in the admin panel so I can change ad banners. It also won’t let me display ad banners in widgets or in AdServe unless I upload them into WordPress and use the site’s own file management structure for images.

Any ideas?