It depends. Do you have control over this remote site? If yes, there are a number of ways that you can get this done.

The easiest seems to be to enable directory browsing in your web browser, and parse its output. FTP would also be easy.
Or, if you want to make it fancy, you can use SOAP and run a subroutine in the image server that'll return the contents of the folder you want, on that remote server.