The cache storage method had been significantly improved in YetiShare v4.0. Cached files, screenshots etc are all now managed in 1 location which means they can easily be removed when uploaded files are deleted.
All other plugins automatically use the new storage method however any screenshots captured by the media converter plugin prior to v4 need migrating using the attached script.
To run following this guidance on your pre v4 installation. You can run this after v4 is installed however you need to update the path to master.inc.php in this file.
Note: The old cache also contains thumbnail versions which don't need migrating, so you may end up with less files in \core\cache\. These will be auto generated again when the thumbnail is requested. Only the original screens are migrated.