Image gallery - resize the images, not the slideshow

I’m working on an xml driven flash website where clients can modify an xml file directly to change the appearance of the site (eventually i’ll make a flash/php dashboard GUI). The site will have listings each with a photo.
I’m trying to find a way around having the clients have to crop images to thumbnail and enlarged view size themselves. In other words the images would be displayed scaled to fit within a movie clip. Does anyone know if this is even possible? It seems that an image is an image at its pixel dimensions and there’s no real way around that…

I guess my target demographic is pretty tech savvy (relatively) and could probably crop images with a basic image editor… it would be nice to find them some kind of batch processor or something. Although at the most clients will probably only add five or ten listings a month or so. if anyone has any insight into this dilemma that would be appreciated!