Seam carving

Seam carving is an image resizing algorithm developed by Shai Avidan and Ariel Shamir. This algorithm alters the size of an image by intelligently removing pixels from (or adding pixels to) the image that carry little importance.
The algorithm determines the least noticeable paths from one side of an image to another, called seams, and cuts the image along those seams. These paths are not straight, but follow the contours of the content in the image. This is why the technique is also called Content Aware Image Resizing.
The importance of a pixel is generally measured by its contrast compared with its neighbor pixels. Additionally, it's possible to define areas of high importance in which pixels may not be deleted, and conversely, areas of zero importance which should be removed first.
With this technique, it's now possible to reduce or enlarge pictures and still retain the details.
Adobe has integrated this technology as an image transformation option in Adobe Photoshop CS4.