I had to perform a similar task with a jQuery plugin I created. It keeps state for an inputs text value, but the principle could easily be used for your width and height.
I would create a custom object that stores the original object's ID, Width and Height. That object is then put into an array. When required to restore the value simply loop the array of custom objects to match ID and bingo, an object with the original width and height.
You can check out my plugin's code at www.wduffy.co.uk/jLabel to see how I implemented this. Depending on how many images you are changing the array could become a little on the heavy side though.
An example might look like
var states = new Array();
function state($obj) {
// Public Method: equals
this.equals = function($obj) {
return $obj.attr('id') == this.id;
};
// Public Properties
this.id = $obj.attr('id');
this.width = $obj.attr('width');
this.height = $obj.attr('height');
};
function getState($obj) {
var state;
$.each(states, function() {
if (this.equals($obj)) {
state = this;
return false; // Stop the jQuery loop running
};
});
return state;
};