1. A method of analysing an image represented by an ordered set of elements (x i ) each having a value, the method comprising for each of a plurality of root positions (x 0 ), repeatedly performing the steps of: selecting a first plurality of elements (x i ) from the ordered set; for each selected element (x i ), selecting a second element (u i ) such that the selected second element has a vector position relative to the root position that is scaled by a factor (α) in comparison with the position of the first selected element; determining, using a computer system having at least one processor, whether the selected elements meet a match criterion requiring that the value of each of the first elements is similar to the value of the corresponding second element; in the event of a match, updating a similarity score (H) in respect of that root element; and selecting at least one of the plurality of root positions as an indication of the location of a vanishing point of the image wherein the at least one selected root position is associated with a peak in the similarity scores (H).