Get image width and height

I'm sure this is an easy one, but here goes:

I am setting up a website using PHP and MySQL. When a customer clicks on an item he/she will be taken to the page where they can view the details, price, larger image, etc.

What I am having trouble with is the larger image part. Using javascript it will pop-up a window with the image inside.

So I am trying to use the php function getimagesize() (and yea I understand how the arrays of that function works). I want to be able to pass the width and height of that to the javascript function.

I keep getting an error message (warning) basically saying it is unable to access the image. I have the image in the database as a path which points to the images folder.

Can you point me in the right direction on this and can I pass these variable to my javascript function?

Sample code would be quite helpful.