The top two reasons why images don't import correctly is because:
1) They were not imported directly from the camera's memory card. No other software or application (Lightroom, Photoshop, Aperture, etc) can be used in between the camera's memory card and Tagger. Always use Tagger to import the images directly from the memory card.
2) The naming convention the camera defaults to naming the images might be one that our tagger system doesn't recognize. If your images are named something like "IMG_0001" then this should not be an issue for you.