Allow The ResizeImage() To Work On ALL Images?

I was having an issue earlier with filling a div depending on window size. I've almost resolved the issue except that it only works on the first instance of the element. For example, I am using the following:

Code:
function resizeImage()
{
var window_height = document.body.clientHeight;
var window_width = document.body.clientWidth;
var new_height = (window_height - 255) + "px";
[Code]...

Which works perfectly, except only with the first image with the id 'gallery-img'. I have about ten on the page, and they generate from a folder on the server via PHP (see below).

[Code]....

I'm not very fluent in JavaScript, but I know there is a way to make this work. how to allow the resizeImage() to work on ALL images?