The JSON format natively doesn\'t support binary data. The binary data has to be escaped so that it can be placed into a string element (i.e. zero or more Unicode chars in d
yEnc might work for you:
http://en.wikipedia.org/wiki/Yenc
"yEnc is a binary-to-text encoding scheme for transferring binary files in [text]. It reduces the overhead over previous US-ASCII-based encoding methods by using an 8-bit Extended ASCII encoding method. yEnc's overhead is often (if each byte value appears approximately with the same frequency on average) as little as 1–2%, compared to 33%–40% overhead for 6-bit encoding methods like uuencode and Base64. ... By 2003 yEnc became the de facto standard encoding system for binary files on Usenet."
However, yEnc is an 8-bit encoding, so storing it in a JSON string has the same problems as storing the original binary data — doing it the naïve way means about a 100% expansion, which is worse than base64.