I don't know if it's possible to get the dimensions of an image like that. I think there may be another way though. Put all of those images (unformatted) in a div whose .style.display='none' so it is hidden. Once they are all there, grab the actual dimensions of each one and use a little math to calculate the new width and height and resize the image. When you are finished with that, reset .style.display='block' or whatever else you use to make it visible again.

Hope that helps.