WhatIsIt is a simple utility for identifying files against a list of signatures. For a file where we know that the size is correct that is a simple matter. When the object in question is a file that is padded or a disk partition or unpartitioned space on a device it's slightly more complicated. The utility is available for both Win32 and Android.
Download whatisit.exe for Win32
Download whatisit for Android
Note that this particular u-boot has 1024 (0x400) bytes of unused IVT at the head.
Note that this last does not use an offset as the file happens to be the correct one without IVT.
Currently the list of signatures is internal and includes various images for B&N NST and Glow models. There will be an update for importing lists of signatures.