Hack to add circle to UIImagePickerController Credit: https://gist.github.com/andreacipriani/74ea67db8f17673f1b8b

UIImagePickerControllerWithCircleOverlay.swift

    /* Usage:
        // This is in your viewcontroller, which implements UINavigationControllerDelegate
        func navigationController(navigationController: UINavigationController, willShowViewController: UIViewController, animated: Bool) {
            if isImageViewer(navigationController) {
                addCircleOverlayToImageViewer(willShowViewController)
            }
        }
    */
    
    func isImageViewer(navigationController: UINavigationController) -> Bool {
        if (navigationController.viewControllers.count == 3 &&
            (navigationController.viewControllers[2].dynamicType.description() == "PUUIImageViewController" ||
             navigationController.viewControllers[2].dynamicType.description() == "PLUIImageViewController")) {
            return true
        }
        
        return false
    }

    func addCircleOverlayToImageViewer(viewController: UIViewController) {
        let circleColor = UIColor.clearColor()
        let maskColor = UIColor.blackColor().colorWithAlphaComponent(0.8)
        let screenHeight = UIScreen.mainScreen().bounds.size.height
        let screenWidth = UIScreen.mainScreen().bounds.size.width

        var plCropOverlayCropView: UIView? //The default crop view, we wan't to hide it and show our circular one
        var plCropOverlayBottomBar: UIView? //On iPhone is the bar with "cancel" and "choose" button, on Ipad is an Image View with a label saying "Scale and move"
    
        if UI_USER_INTERFACE_IDIOM() == .Pad {
            plCropOverlayCropView = viewController.view.subviews[1]
            plCropOverlayBottomBar = viewController.view.subviews[1].subviews[1]
        
            // Protect against iOS changes...
            if plCropOverlayCropView != nil && plCropOverlayCropView!.dynamicType.description() != "PLCropOverlay" {
                print("Image Picker with circle overlay: PLCropOverlay not found")
                return;
            }

            if plCropOverlayBottomBar != nil && plCropOverlayBottomBar!.dynamicType.description() != "UIImageView" {
                print("Image Picker with circle overlay: PLCropOverlayBottomBar not found")
                return;
            }
        }
        else {
            plCropOverlayCropView = viewController.view.subviews[1].subviews.first
            plCropOverlayBottomBar = viewController.view.subviews[1].subviews[1]
            
            // Protect against iOS changes...
            if plCropOverlayCropView != nil && plCropOverlayCropView!.dynamicType.description() != "PLCropOverlayCropView" {
                print("Image Picker with circle overlay: PLCropOverlay not found.")
                return;
            }
            
            if plCropOverlayBottomBar != nil && plCropOverlayBottomBar!.dynamicType.description() != "PLCropOverlayBottomBar" {
                print("Image Picker with circle overlay: PLCropOverlayBottomBar not found.")
                return;
            }
        }
    
        //  It seems that everything is ok, we found the CropOverlayCropView and the CropOverlayBottomBar
        plCropOverlayCropView!.hidden = true //Hide default CropView
    
        let circleLayer = CAShapeLayer()
        let circlePath = UIBezierPath(ovalInRect: CGRectMake(0, screenHeight/2 - screenWidth/2, screenWidth, screenWidth))
        circlePath.usesEvenOddFillRule = true
        circleLayer.path = circlePath.CGPath
        circleLayer.fillColor = circleColor.CGColor
        
        // Mask layer frame: it begins on y=0 and ends on y = plCropOverlayBottomBar.origin.y
        let maskPath = UIBezierPath(roundedRect: CGRectMake(0, 0, screenWidth, screenHeight), cornerRadius: 0)
        maskPath.appendPath(circlePath)
        maskPath.usesEvenOddFillRule = true
    
        let maskLayer = CAShapeLayer()
        maskLayer.path = maskPath.CGPath
        maskLayer.fillRule = kCAFillRuleEvenOdd
        maskLayer.fillColor = maskColor.CGColor
        viewController.view.layer.addSublayer(maskLayer)
    
        // Re-add the overlayBottomBar with the label "scale and move" because we set its parent to hidden (it's a subview of PLCropOverlay)
        viewController.view.addSubview(plCropOverlayBottomBar!)
    }

I diverged a bit from the original. You're welcome to look at the history of the gist.