The Awesome Resizer is a freeware application that allows quick dynamic resizing of any image and much much more.
It works like this:
* Drag'n'drop an image.
* Resize the image's window.
* Choose a manipulator, like 'Drunk' and click on 'Apply' a few times.
* To save under the chosen file name and format, drag'n'drop the image, for example on the Desktop.