Hugin is free open source, an easy to use cross-platform panoramic imaging toolchain based on Panorama Tools. Hugin allows you to assemble a mosaic of photographs into a complete immersive panorama, stitch any series of overlapping pictures and much more. Hugin will attempt to find points on the images that match up with each other, or you can manually specify control points.
There are over 8,000 images on Flickr that’ve used Hugin for assembling amazing panoramic shots. Once you get the hang of using the program you’ll be able to create shots using Hugin like this that started out with this panoramic.
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