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Ever have to crop or resize a picture to fit it better on a web site but end up disappointed with the content you have to lose from the photo? Using a method called liquid rescaling, your pics can be rescaled while retaining almost all of the pertinent content, so you can get the best of both worlds—a smaller image that retains everything you want. If it still sounds a little unclear, check out the video to see this brilliant idea in action.
If you're a fan of the open source image editor GIMP, you can download and install the Liquid Rescale GIMP plug-in to get liquid rescaling results (after you install it by moving the downloaded files into your GIMP directory, you'll see the Liquid Rescale option under the Layer menu). If you don't feel like installing anything, you should try out the Rsizr webapp, which does the rescaling from the comfort of your browser. Both tools are a good deal slower than what you see in the very cool video above, and neither are implemented to the full extent of what you're seeing in the video, but the results are still promising.