Transliteration | drupal.org

Searched for "ampersand breaks imagecache" and ultimately found this module. An & (and probably other special characters) makes a perfectly valid uploaded file but does not show up in that file's imagecache manipulations.

Provides a central transliteration service to other Drupal modules, and sanitizes file names while uploading.

Generally spoken, it takes Unicode text and tries to represent it in US-ASCII characters (universally displayable, unaccented characters) by attempting to transliterate the pronunciation expressed by the text in some other writing system to Roman letters.