You shouldn't really have lost any "active" posters or fanart, that's a bit odd. Should be easy enough to re-cache though (as long as the originals remain available).
Texture Cache Maintenance Utility: Preload your texture cache for optimal UI performance. Remotely manage media libraries. Purge unused artwork to free up space. Find missing media. Configurable QA check to highlight metadata issues. Aid in diagnosis of library and cache related problems.