Decoding binary data stored in XML by a third party tool

I'm trying to parse XML files produced by a third party tool ( [HTC Sync Manager][hsm] ) , since said tool refuses to work anymore.

XML parsing is simple enough, but I'm stuck with trying to decode binary image data serialized into those XML files. As an example, I have a 886 character string which I know represents an image. That strings starts with

rb/Q7XTbM16/8AsiXViZ7rWtGN1qN/dd/+Pe2r4R/ZX/bC0O6/ZiufgzfC5tr+51i6ubO7u

Base64 decoding it leads to garbage, so that's not the answer.

How can I decode this kind of data?