explorador - 5:23 am on Mar 31, 2011 (gmt 0)
Been there :( pretty sad reality and few options.
Watermarking images is a good option, it spreads your brand and also makes it harder for others to use them just like that. I'm not so much into flash galleries but they are a good option, just remember the watermark, why? because it is very easy to hit print screen to capture the image and paste it in some photo editing software to crop it.
You could also use some folder structure to organize the images while keeping all of them named equal, it gives people a hard time when saving your images to disk as the computer will ask for an overwrite. But anybody can still get them by capturing the screen.