Prerequisites:

• inline module
• lightbox2 module
• imagecache module

You simply enable lightbox v2 on image nodes (admin/settings/lightbox2) but your lightbox show a small imagecache thumbnail?

• Disable lightbox on image nodes (admin/settings/lightbox2)
• Enable “Display image with a link to the image file” (admin/settings/inline)
• Apply this Inline lightbox patch

This patch simply add a rel=”lightbox” to each inline image link, natively pointing to full-size image.