Hey Sevex,
The height and width of an image are stored inside the image and each image type (jpg, gif, bmp, png, ..) stores this differently. The best way to do this is to find a custom tag which can read the image formats you're interested in and have it run after the <cffile> upload. I would take a look in the Allaire Custom Tag Gallery as I'm sure someone has written a tag to retrieve the height & width from the popular formats.
Good luck,
GJ