This is general usage:

resizer.php?imgfile=<http path to file>&max_width=<width px>&max_height=<height px>

Hello Taras,

As explained in the FAQ, the script itself can call the resizer if you set the option useThumbGenerator to true. (Granted that lives in the same folder than your current page).

However, if you want to call it yourself, just call the script like this: "resizer.php?imgfile=whatever.jpg&max_width=200&max_height=400".
The jpeg file being in a path relative to the script's one, and the sizes being optional (you should have at last one set).

The resizer uses a folder named "cache" to save the images he already resized. This folder should be writable by the script and be localized as a child of the same folder he lives in.

You can replace it with any script you like, as long as you use the standard way of giving the full image and thumbnail path to the script.