If you're targeting Lion you can subclass IKImageBrowserView and override the draggingSession:sourceOperationMaskForDraggingContext: NSDraggingSource protocol method. To prevent drags outside of your application just return NSDragOperationNone if the context is NSDraggingContextOutsideApplication. Otherwise, return the dragging operations that you're interested in. This way you can disallow drags to the desktop, Finder, etc. but still permit drags within your application's image browser view.
- (NSDragOperation)draggingSession:(NSDraggingSession *)session sourceOperationMaskForDraggingContext:(NSDraggingContext)context {
[super draggingSession:session sourceOperationMaskForDraggingContext:context];
switch (context) {
case NSDraggingContextOutsideApplication:
return NSDragOperationNone;
break;
case NSDraggingContextWithinApplication:
return NSDragOperationAll;
break;
default:
return NSDragOperationAll;
break;
}
}