You need more info from the vendor
You need to ask them what the imageData points to. Is it a bitmap or a a DIB or is it a jpeg or something else?
Once you know this, you will still have to research how to access it, but at least someone can help you with that. Whithout the extra info, it's impossible to know what imagedata represents I think.
Also, what is imagesize? The number of bytes used to render the image? It is meaningless unless they provide you with the data structures as well...
Cheers
Paul Lewis