Cracking vigenere of non-text cleartext
AFAIK vigenere cipher is a plain subsitution algorithm with arbitrary key length, destroying statistical patterns (f.e. of natural languages) but not conducting any transposition.

Btw. a classic approach to crack a vigenere cipher is the Kasiki-Test (https://en.wikipedia.org/wiki/Kasiski_examination) which might give you information reagrding the key length. 

If you try to decrypt a file format (jpeg, gif, zip etc.) you actually know at least the first bytes (fileheader) as they are defined by convention:
f.e. a zip file always starts with 0x04034b50 (https://en.wikipedia.org/wiki/Zip_%28file_format%29) which gives you the first 4 bytes for your decryption table.