Images, JavaScript, and Flash files that PHP sends to the browser are not affected by the GPL because they are data. However, Drupal's JavaScript, including the copy of jQuery that is included with Drupal, is itself under the GPL as well, so any Javascript that interacts with Drupal's JavaScript in the browser must also be under the GPL or a GPL compatible license.
mooZoom is an unobtrusive javascript utility that allows you to zoom an image in the desired point using mouse-scroll. It does not break the layout of the page and it's cross-bowser (ie, opera, firefox, safari).
J. Merelo, A. Garc\'ıa, J. Laredo, J. Lupión, и F. Tricas. Proceedings of the 2007 GECCO conference companion on Genetic and evolutionary computation, стр. 2851--2858. New York, NY, USA, ACM, (2007)