1. A computer based method for estimating a thin plate spline (TPS) warp between two digital images of a sequence of digital images representing one or more physical objects, the digital images comprising pixels, the method comprising: receiving first and second digital images of the sequence of digital images; determining a fixed template region within said first image; positioning a fixed set of reference points within said fixed template region; determining a first set of pixels within said second image, said first set of pixels corresponding to said fixed template region and including a set of projections of said fixed reference points; determining a TPS parameter vector from said set of projections; determining a back-warped image by warping said first set of pixels based on said TPS parameter vector.