You got a .rar file and you don't how to open it, some one asked you to send him "a rar file" or you just need a good archiving software? Download and install WinRAR.
Truly amazing work by the NYC Grid guys creating images composed of two images at the exactly same location only decades or sometimes even century apart.
In Photoshop CS6, the new version of Photoshop, you can use special cropping tool and you are done, but that doesn't mean you cannot achieve the same result with older versions.
Abraham Lincoln was American president during American Civil War. He also fought against slavery and is one of the most important presidents in the American history.
Remember the legendary Predator movie with Arnold Schwarzenegger? Those Predator aliens had this thermal view feature so they could their prey even in complete darkness, let's Photoshop it.