6. The method of claim 1 , wherein determining a rank score for each of the two or more distinct book content items comprises: representing the two or more distinct book content items as a graph in computer memory, where each of the distinct book content items is represented as a distinct node in the graph and where an edge exists in the graph between each pair of distinct nodes that represent distinct book content items that both include a similar image; and determining a rank score for each of the two or more distinct book content items based on the edges between the distinct nodes.
6. The method of claim 1 , wherein determining a rank score for each of the two or more distinct book content items comprises: representing the two or more distinct book content items as a graph in computer memory, where each of the distinct book content items is represented as a distinct node in the graph and where an edge exists in the graph between each pair of distinct nodes that represent distinct book content items that both include a similar image; and determining a rank score for each of the two or more distinct book content items based on the edges between the distinct nodes. 8. The method of claim 6 , wherein representing the distinct book content items as a graph in computer memory comprises: representing the book content items as a weighted graph in the computer memory, the weighted graph including a plurality of distinct nodes, each distinct node representing a corresponding distinct book content item in the plurality of distinct book content items, each edge in the weighted graph being weighted based on a relative importance of the distinct node from which the edge originates; for each distinct node: identifying matching image content in image content of other distinct book content items that are represented by other distinct nodes, each matching image content being image content that has descriptor points that match the corresponding descriptor points of image content in the distinct book content item corresponding to the distinct node; generating edges in the weighted graph connecting the distinct node to other distinct nodes corresponding to the other distinct book content items, each edge representing one or more matches of image content in the distinct book content item to matching image content in another distinct book content item.