Opens the image file to extract the width and height values and then immediately closes the file. This is much faster than loading the entire image. This can be useful when using LoadImageResized to know how much to scale the image before loading it. Both the width and height will be returned in a single integer value, the top 16bits will be the width and the lower 16bits will be the height. You can extract these values in Tier 1 by doing 
 width = result >> 16
 height = result && 0xFFFF 
integer GetImageSizeFromFile( filename )