View goes out of a View Boundary

I have a Background view (UIImageView) in that i am adding a view(UIView). this contentView(UIView) contains UIPanGestureRecognizer.

I am giving UIPanGestureRecognizer to contentView by bellow code :

UIPanGestureRecognizer *panRecognizer = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(movePhoto:)];
[panRecognizer setMinimumNumberOfTouches:1];
[panRecognizer setDelegate:self];
[contentView addGestureRecognizer:panRecognizer];
[panRecognizer release];

and then i am adding this contentView to Background View (UIImageView) by bellow code :

[imgBG addSubview:contentView]; // here imgBG is Background view.

but when i move this contentView it goes out of imgBG.

bellow is the method to move contentView

    [[[(UITapGestureRecognizer*)sender view] layer] removeAllAnimations];

[self.view bringSubviewToFront:[(UIPanGestureRecognizer*)sender view]];
CGPoint translatedPoint = [(UIPanGestureRecognizer*)sender translationInView:self.view];

if([(UIPanGestureRecognizer*)sender state] == UIGestureRecognizerStateBegan) 
{
    firstX = [[sender view] center].x;
    firstY = [[sender view] center].y;
}
translatedPoint = CGPointMake(firstX+translatedPoint.x, firstY+translatedPoint.y);
[[sender view] setCenter:translatedPoint];

CGFloat finalX = [sender view].center.x;
CGFloat finalY = [sender view].center.y;
[[sender view] setCenter:CGPointMake(finalX, finalY)];

I think, here the contentView should remain inside the imgBG as it is the subview of imgBG.

Please let me know whether there is a problem in my code or its due to UIPanGestureRecognizer.

thanks in advance.

I just had to do :

[imgBG setClipsToBounds:YES];