Byte[] property type

One of the REST APIs we need to call takes one of request parameter as a byte array. I am trying to create a message class and couldnt figure out which is equivalent type that corresponds to Byte[]. I need to read from a jpg file and then convert it to byte[] before i invoke this webservice. Appreciate if anyone can point me in the right direction. I can use %Stream.FileBinary class to store the jpg file after loading from a file. trying to figure out how to convert that to byte[].

Thank you,

Ravi