I think what Lala_G_Clef_Jewelry mentioned points to the problem. Light Box seems to read large sized images from the images/large folder. IH2 places large (and other) images in the weird bmz_cache folder using a filing system I'm not too familiar with.

Unless either Light Box can take images from the IH2 folders, or unless IH2 can place large images in the images/large folder, I don't know that these two would be able to work together.