1. A method of analyzing a known image abstraction and a query image abstraction to determine whether a query image is similar to a known image, the method comprising: accessing the known image abstraction, the known image abstraction being based on part or all of the known image; accessing the query image abstraction, the query image abstraction being based on part or all of the query image, the known image and the query image being of a same type; combining at least a part of the known image abstraction with at least a part of the query image abstraction to generate a combined image abstraction; comparing the combined image abstraction with at least a part of one or both of the known image abstraction and the query image abstraction; and determining whether the query image is similar to the known image based on comparing the combined image abstraction with at least a part of one or both of the known image abstraction and the query image abstraction, wherein the known image abstraction comprises a known covariance matrix: wherein the query image abstraction comprises a query covariance matrix; and wherein combining at least a part of the known image abstraction with at least a part of the query image abstraction comprises combining the known covariance matrix with the query covariance matrix.