igzoom v2 uses the same method that i use for zoomed speed boxes where a top level layered window doesnt count for what is captured using a bitblt screencapture. See for yourself; use this example: http://www.thescarms.com/vbasic/capture.asp and try to screenshot my igmod windows (for the menu or the speed). You can't because the layered effect is in place.
Using that if your window was actually on top of the iguidance window (not same parents but a top level window) iguidance will still redraw and not cover up your window, and you can poll the contents into memory somewhere to do your png effect.
I would make you a sample function but a: I dont know delphi and b: i have had one too many drinks tonight to think on that kinda stuff. I have some freetime tommorow though, so ill try to make an example function that quickly alpha blends 2 images together (it will be in vb6, but ill try to make it simple enough that you can adapt it)