While I'm not sure the exact best way to do it, in this thread:
http://www.68classifieds.com/forums/...ead.php?t=1314
I suggest having the ability to lasso and upload multiple images at once. With that feature and a decent connection, you could probably add images for 50-100 ads in an hour or so, depending on how efficient you can make the user interface.
With the current system and multiple images per ad, it would take much longer.