Generally - the first thing the server will do when you put in this address is look for an index file in the folder. If one is there it will execute the index file. If not, based on the configuration, it will either give you a 404 or show you the folder contents.
abraham is right but regardless I dont think this wouldnt be the best way to do something like that. You should either A create a gallery using dreamweaver, photoshop flash etc... or simply just zip all the pictures up and place them on the server. ex. http://www.mywebsite.com/pictures.zip this way the will just download to the clients machine and they will be able to view them all in the viewer slideshow as opposed to one image at a time.