Change g->image alt text?

Hi. Sorry if this is easy and I'm pretty new to Gallery 2, but for the life of me I can't figure this out nor find anything via searching here or Google.

When Gallery displays an image in an album it inserts the item title as the html img alt text. I need it to display the item description as I'm using jquery/fancybox to overlay album imagery on the page and want the "caption" to be the item description.

Here is the code that Gallery uses to generate the <img> tag:

{g->image item=$child image=$child.thumbnail class="giThumbnail"}

Now I know that $child is the array where the alt title txt is being taken from, but despite my lengthy attempts at searching the code base I cannot find where g->image actually explodes the array and builds the html. Etc.

Thanks for any tips!!!