There are IE specific ActiveX controls (or something similar but I know little about them) that give you access to the local file system from which you might be able to view a file's properties. But unless you know exactly what you are doing there are all sorts of security risks doing it this way and so I would not recommend do it this way.
As has already been mentioned, you really need to upload the image first after which you can get the image's actual pixel width and height.
An option you could use, which would make it appear to the user the image dimensions are being displayed prior to uploading is:
1- put an onchange event handler on your <input type="file" /> which uploads the file to the server into a temp area.
2- the event handler then polls the temp area at set intervals with an ajax request to check for the existance of the image file name. If it exists, then return the image's pixel width and height from the appropriate php functions and display them in the browser. Then delete the temp image file.
All this can be done without a page refresh and the user will see the image's dimensions displayed in the browser when they select an image file to upload.
Or maybe you can get the browser's viewport dimensions and then size your images accordingly.