There are plenty of tools around which will calculate file hashes for you (values which represent the digital fingerprint of a file), but most aren't so convenient to use. You'll typically have to launch that particular program, import the files, choose the options you need, manually copy the hash value, and so on.
HashTab makes all this considerably simpler, though, by just displaying your required hashes right in the file Properties dialog.
Once the program is installed, for instance, just right-click something, select Properties > File Hashes, and you'll see the CRS32, MD5 and SHA-1 hashes for that file.
Not what you need? Click Settings for a full list of the functions on offer: Adler32, CRC32, MD2, MD4, MD5, RIPEMD(128,256,320), SHA-1,256,384,512, Tiger, and Whirlpool. Check the boxes next to your preferred options and they'll be available next time.
Once your hash is displayed in the dialog, you can copy it to the clipboard by right-clicking the value and selecting Copy (you get a magnet URL option here, too).
And there's even a "Compare a file" option which allows you to hash other files for an immediate comparison.