A method (500) of determining rotation and scale transformation parameters is disclosed. The method (500) determines a plurality of weight values associated with one or more parts of at least one of a first and second image (e.g., 154. 155). A representation of each of the first and second images (154. 155) is formed using the weight values, the representation being substantially invariant to translation of the first and second images (154. 155). Rotation and scale transformation parameters relating the first and second images (154. 155) are determined based on the representation of each of the first and second images (154. 155). The rotation and scale transformation parameters are stored.