I actually don’t know of anything that is a perfect solution for this. I know there are some photo-blogging specific applications that might do the trick, with (maybe?) less hassle than customizing WordPress for this.
I’m actually looking into taking up a new project and this seems like a pretty promising idea…
I’m using Autoviewer on a site I’m developing. It uses an XML file to determine what images to load. Should work well for that. Both the free version and $40 version use the XML file, so you should be good either way (I think). Changing the filenames in the xml file should be pretty easy to teach to just about anybody… hopefully :)
If you know youre stuff it is very customizeable and if your client is anything like the Contractors I have done work for WordPress will be too much for them to deal with. Especially if its for just images.