Prevent user from taking screenshot?

Question

Hey everybody.
I have a small problem here with a game/program I am developing.
The whole game is supposed to work like this:
"http://en.wikipedia.org/wiki/Concentration_(game)"
I have an Image in the background that the user can see after clearing all cards on the screen. The picture was made by our in-house artists, thats why we dont want them floating around everywhere.
A google and forum searcg turned up without results
Now is there any way to prevent the user from just taking a screenshot from the backgroundpicture and share the pictures everywhere?
Is there a flag or property that I can set to prevent screenhots beeing taken from my application?
Anything?
I hope somebody can help.

Answer 1

I have a thought regarding this, seems like a long shot but it just might lead to something.
When programming in Cocoa on the Mac, I noticed that when you try to get the contents of an NSView object as a PDF (there's a method that does this, forget the name), the view's drawRect method gets called to render the contents. So theoretically you can design a view to sense that its contents are being captured and render itself differently (with higher resolution for example might make sense in some applications; or not render at all as in your case).
It may be that something like this could work for you. The difficult part is having the view that draws your sensitive image sense whether the drawRect is called for legitimate screen drawing or for drawing into a bitmap as may happen when trying to take a screenshot. Perhaps you could examine the innards of the graphics context in some way to achieve this? Or you could set a flag somewhere in your code whenever you call the view's setNeedsDisplay method, and in drawRect only render the image if that flag is set.
Of course, we don't know the mechanism the iPhone uses for taking screenshots, it's possible that it all happens on a lower level of the operating system and the screen image is simply directly copied to a bitmap in which my suggestion will not work.
Anyway it's an interesting question, let us know if you figure it out.