Go to Settings > Apps > (touch the 3 point in the up-right corner) Show System processes (or something like that, I translate from french) > Media Storage > Storage* > Clear DATA.
Don’t be afraid, it has something to do with the way that your fp organizes the data (so it doesn’t affect your data, just the way your phone sees it).
NOTE: It is important to let your fp rebuild his ‘library’ so wait at least 10min