Your going to want to do it via html/PHP. You can specify size, extensions, etc. If you have used PHP before this isn’t a big deal.
Here is a link to the PHP documentation.
if you haven’t used PHP You may want to look at one of the Photo management systems like Coppermine (Which I use for baby pictures, but there are several) to help manage the photos.
I40.com - Home Page
MP3Mystic - Personal Streaming Music server.
(Neither of these sites are still hosted at dreamhost)