1. A method, comprising: accessing image data for an image sequence of a subject scene, the image sequence comprising a plurality of images captured at different respective times, the image sequence capturing relative movement in the subject scene between a foreground feature and a background during a time span of the image sequence; selecting from the image sequence a reference image that comprises a foreground portion and a background portion, the foreground portion capturing the foreground feature; in an automated operation using one or more processors, deriving from the image data spatially varying blur parameters for at least part of the background portion, wherein the spatially varying blur parameters include a plurality of blur kernels; and generating a modified image by blurring the background portion of the reference image based on the spatially varying blur parameters, to simulate the relative movement of the background during the image sequence time span, the modified image having a substantially unblurred foreground portion relative to the reference image.