One factor is whether or not you want a slideshow and if you want nice transitions in it.
Video CD's can show off digital photos nicely, even in slideshows -- as long as you are not using any animated transitions. Animated transitions are basically a form of a movie, and CD's do not do movies well - if at all. (Depends on the format).
DVD's, on the other hand, allow fancy slideshows with animated transitions between photos, nicer animated menus - like a menu full of appealing graphic buttons that change color or appearance when you mouse-over them, and that point the viewer toward a given slideshow when Enter is pressed on the TV Remote Control. Some of the spectacular-looking slideshows - like those created with SimpleStar's PhotoShow Deluxe V. 5 (See a working PhotoShow Deluxe gallery here
), are actually SWF slideshows (the best-looking, IMO) and cannot be reproduced on TV using Video CD's.