Lamento contradecirte, pero creo que estas equivocado:
http://www.php.net/function.getimagesize
getimagesize
(PHP 3, PHP 4, PHP 5)
getimagesize -- Get the size of an image
Description
array getimagesize ( string filename [, array &imageinfo] )
The getimagesize() function will determine the size of any GIF, JPG, PNG,
SWF, SWC, PSD, TIFF, BMP, IFF, JP2, JPX, JB2, JPC, XBM, or WBMP image file and return the dimensions along with the file type and a height/width text string to be used inside a normal HTML <IMG> tag.