Can we decode the Hash that is generated by MACTripleDes

Actually i want to send an image from client to server in the Encrypted smallest possible size.

Is there any other method to do that

A hash is a secure checksum of data, it cannot be "decoded".

You're probably looking at encryption and compression. Compressing first will generally give you a smaller final size.

Check out the System.IO.Compression namespace for built-in methods of compressing data.

Check out the System.Security.Cryptography.CryptoStream for example of encrypting/decrypting data.