Disable Cache or Clear Cache

Im using WPThumb to build images for a slideshow

echo '<li><img src="'.wpthumb( $propertyimg, 'width=600&height=400&crop=1&cache=false' ).'" border="0"/></li>';

These images are likely to update but their filenames stay the same.

Im trying to set cache to false so that a cache/local version is not created. But it always seems to create a local version.

1> Is it possible to prevent caching?
2> Is it possible to clear the cache entirely so that all images are rebuilt?

https://ww.wp.xz.cn/plugins/wp-thumb/