1. A system, comprising: an extraction module extracting contextual information from an image of an area of interest including annotations; a feature selection module building a current feature vector using the extracted contextual information and the annotations; and a referencing engine computing a similarity score between the current feature vector and a prior feature vector of a prior image, wherein the similarity score (D) is computed as a weighted sum distances (d i ) between each element (m i ) the current feature vector and the prior feature vector, wherein: 
 D=Σm i *d i ; and wherein distances (d i ) of annotation (a i ) and (b i ) are computed as: 
 d i =e a i -b i *e a′ i -b′ i .