Hugin

Hugin is a cross-platform open source panorama photo stitching and HDR merging program developed by Pablo d’Angelo and others. It is a GUI front-end for Helmut Dersch’s Panorama Tools and Andrew Mihal’s Enblend and Enfuse. Stitching is accomplished by using several overlapping photos taken from the same location, and using control points to align and transform the photos so that they can be blended together to form a larger image. Hugin allows for the easy (optionally automatic) creation of control points between two images, optimization of the image transforms along with a preview window so the user can see whether the panorama is acceptable. Once the preview is correct, the panorama can be fully stitched, transformed and saved in a standard image format. Wikipedia