I found the source of the problem. It's the .htaccess in your albums directory with the "Options All -Indexes" directive set. As I've discovered with a little bit of digging around, the apache on the VPS appears to actually be a slightly older version that conflicts with this. I've got a bug in with our admins to get this fixed for you as soon as possible. In the mean time I've got this working just by changing the directive to "Options -Indexes" which should still block out users from listing the contents of this subdirectory and doesn't cause any conflicts with the current version of apache in there. We'll keep you posted once your apache is updated so that you can change this back to "Options All -Indexes" if you'd like.

He probably fixed the one instance where I had manufactured the test case. It's now showing most of the images, but not all. (How many? No clue. Nor any idea how it serves one image but not another one in the same directory.)

Sometime today I'm going to have to copy and update every htaccess I've got, then figure out what other directives don't work with the current Apache ... then update fucking Apache, of course.