Answer by Graham Dunnett

The Unity application side of this is documented here: http://docs.unity3d.com/ScriptReference/Texture2D.LoadImage.html The displaying a window, and loading a chosen image into a byte array can be handled using non-Unity c# code. So maybe write a c# application that does this task. Once you have that working, add the script you've written into your Unity project. (Obviously you won't need the basic application startup code.)