[akdas]

Good question. I talked about it in my previous article, but the gist is I compute the energy (or costs in this case), then use dynamic programming to find the new lowest energy seam each time. This allows a subsequent seam to pass through an earlier seam, as seams are found based on the latest images, where pixels have been pushed together from previous removals.

However, you'll notice that the costs are only changed in a small area around the removed seam, so if I optimized the process, I could avoid recomputing costs for the majority of pixels.