Seam carving, otherwise known as content aware image resizing, is one of the most impressive features available in the latest version of Photoshop. Basically what it does is allow you to change the aspect ratio of an image, while avoiding the drawbacks of cropping or scaling, where parts of the image can be lost or distorted. Moreover, it's possible to manually define protected areas in which pixels may not be removed or conversely designate pixels that must be deleted.

the algorithm was developed by Shai Avidan and Ariel Shamir and presented at SIGGRAPH in 2007. In fact, the technique has since shown up in a number of other applications, one of which is Seam Carving GUI. This freeware application doesn't require installation and is fairly easy to use: just load an image, select the area you want to keep or remove when resizing, and select the target size.