Displaying part of an image?

There is no documentation as the imageframe is an internally only used thing. I you want to really use it you must do that within the module itself as some stuff is privated so external access is impossible.

and messing with it can lead to straight crashes if you do not have an idea what you are doing ...
So if you think that Blitz3Ds surface - addvertex etc commands are to complicated, better don't touch it.