Hi barbarosso,
It's been a while since I played this game. Is there more than one bookcase, and are you looking at the correct one? Perhaps the hotspot for the statue is small -- you could try moving your cursor very slowly around the area. If that doesn't work, perhaps check back through Bert Jamin's walkthrough
HERE and see if you can spot anything you might have missed doing up to this point.
The photograph shows two strange symbols at far right. They're all you need to make a note of.