After uploading your image, use the following code to calculate it's size.

<cfscript>
   imageObj = createObject("java", "java.awt.Toolkit");
   imagetools = imageObj.getDefaultToolkit();
   objImage = imagetools.getImage("#file.serverdirectory##file.Serverfile#");
   width = objImage.getWidth();
   height = objImage.getHeight();
</cfscript>

Then use the values how you wish, to store in a database, deny an upload according to sizes etc. The following just outputs the values for info.

<cfoutput>
  width: #width#<br>
  height: #height#
</cfoutput>