Methods, systems, and apparatus, including computer program products are provided for ranking distinct book content items based on implicit links to other distinct book content items. The implicit links are defined based on the identification of matching features in the distinct book content items. In some implementations, the matching features can be image features that appear in image content of the distinct book content items. Edges representing implicit links are generated between distinct nodes representing the distinct book content items in the weighted graph. Each distinct book content item can be ranked based on the edges connected to the distinct node in the weighted graph that represents the distinct book content item.