Image Pop Up Class: Create thumbnails and link pictures in new windows

Comments: This class is designed to ease the publication of images in html webpages that uses PHP.
1) With this class you can insert pictures in your web pages in one line (simlar to <IMG> tags).
2) The class automatically creates a link to the original image using javascript (displaying the selected picture in a new window with the size of the image) and presents a thumbnail in your page.
3) THIS CLASS DOES NOT NEED GD LIBRARY TO WORK, but if you have GD Library 2.0 or later installed it's possible to use the class to create thumbnails on the fly. The detection of the GD library is AUTOMATIC.
4) When GD Library 2.0 or later is not available, the image type is not supported by GD Library or simply when you want to decrease the execution time of your scripts, the class uses the original image as thumbnail and link, modifying its size on the IMGtag.
5) To protect your pictures, you can set up this class to use the images as CSS backgrounds of DIVtags that are creates automatically. In effect, a 100% transparent gif image (null.gif) is used to mask your DIVtag as an image, so visitors will save empty images on their disks.

Files:
1) imgpopup.class.php, containing the class definition.
2) imgpopup.php, for output the Pop Up Window Content.
3) img.php, for output the GD based Thumbnails.
4) imgpopup.js, JavaScript file containing de ImgPopUp Function.
5) null.gif, Transparent GIF used to mask image contents.

Extras:
1) test.php, examples and information about the use of the class.
2) misola.jpg, picture used in test.php (Thanks to Manuel Isola).