Binwalk is a tool for searching a given binary image for embedded files and executable code.
Specifically, it is designed for identifying files and code embedded inside of firmware images. Binwalk uses the libmagic library, so it is compatible with magic signatures created for the Unix file utility.
Binwalk also includes a custom magic signature file which contains improved signatures for files that are commonly found in firmware images such as compressed/archived files, firmware headers, Linux kernels, bootloaders, filesystems, etc.