Front facing camera in UIImagePickerController

You can flip the image from the source image use this

UIImage *flippedImage = [UIImage imageWithCGImage:picture.CGImage scale:picture.scale orientation:UIImageOrientationLeftMirrored];

Edit: Added swift code

let flippedImage = UIImage(CGImage: picture.CGImage, scale: picture.scale, orientation:.LeftMirrored)

I had the same problem - and the solution above only got me half the answer, because the user had to approve the mirrored image before getting to the next page of my app - where I use the captured image after flipping it.

To solve this I had to flip the camera view whenever I switch to the front facing camera:

- (IBAction)flipCamera:(id)sender {
if(cameraUI.cameraDevice == UIImagePickerControllerCameraDeviceFront)
{
    cameraUI.cameraDevice = UIImagePickerControllerCameraDeviceRear;
}
else {
    cameraUI.cameraDevice = UIImagePickerControllerCameraDeviceFront;
}
cameraUI.cameraViewTransform = CGAffineTransformScale(cameraUI.cameraViewTransform, -1,     1);     
}

Just to expand on this great answer, some typical complete code, Dec2013, iOS7 / Xcode5. Does everything. You just need an icon (cameraToggle.PNG in the example).

-(void)showTheDeviceCamera
    {
    if ( ! [UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera] )
        return;

    // self.cameraController is a UIImagePickerController
    self.cameraController = [[UIImagePickerController alloc] init];
    self.cameraController.delegate = (id)self;
    self.cameraController.mediaTypes = @[(NSString *)kUTTypeImage];
    self.cameraController.allowsEditing = YES;
    self.cameraController.sourceType = UIImagePickerControllerSourceTypeCamera;
    [self presentViewController:self.cameraController animated:YES completion:NULL];


        // Add front-rear toggle button MANUALLY, IF NECESSARY
        // (You seem to usually get it for free, on iPhone, but
        // need to add manually on an iPad.)

        UIView *buttonView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"cameraToggle"]];
        [buttonView sizeToFit];

        buttonView.userInteractionEnabled = YES;
        [self.cameraController.view addSubview:buttonView];

        UITapGestureRecognizer *tap =
            [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(_frontRearButtonClicked) ];
        tap.numberOfTapsRequired = 1;
        [buttonView addGestureRecognizer:tap];

        // we'll add it at the top right .. could be anywhere you want
        buttonView.center = CGPointMake(
                self.cameraController.view.frame.size.width-buttonView.frame.size.width,
                3.0 * buttonView.frame.size.height
                );

    }

-(void)_frontRearButtonClicked
    {
    [UIView transitionWithView:self.cameraController.view
        duration:1.0
        options:UIViewAnimationOptionAllowAnimatedContent | UIViewAnimationOptionTransitionFlipFromLeft
        animations:^{
            if ( self.cameraController.cameraDevice == UIImagePickerControllerCameraDeviceRear )
                self.cameraController.cameraDevice = UIImagePickerControllerCameraDeviceFront;
            else
                self.cameraController.cameraDevice = UIImagePickerControllerCameraDeviceRear;
        } completion:NULL];
    }

As the other answers, I had the same problem. As Yonatan Betzer mentioned, just flip the final image is only half the answer, because the preview image, displayed by the UIPickerController when you take a picture with the front camera, it's still inverted (mirrored).

Yonatan Betzer's anwser works great, but he did not mentioned how or where to put the action to change the camera device.

Based in some codes from internet, I created a Pod to get this wanted behavior:

https://github.com/lucasecf/LEMirroredImagePicker

After installed, you just have to call this two lines of code together with your UIImagePickerController:

self.mirrorFrontPicker = [[LEMirroredImagePicker alloc] initWithImagePicker:pickerController];
[self.mirrorFrontPicker mirrorFrontCamera];

And thats it, simply as that. You can check for more informations in the README of the github link.

Just to add how I have just achieved this without subclassing UIImagePickerController and without adding extra buttons to the camera view.

Simply listen for this notification which is fired several times whenever the camera is changed:

[[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(cameraChanged:)
                                                 name:@"AVCaptureDeviceDidStartRunningNotification"
                                               object:nil];

Then use this method to flip the camera view:

- (void)cameraChanged:(NSNotification *)notification
{
    if(imagePicker.cameraDevice == UIImagePickerControllerCameraDeviceFront)
    {
        imagePicker.cameraViewTransform = CGAffineTransformIdentity;
        imagePicker.cameraViewTransform = CGAffineTransformScale(imagePicker.cameraViewTransform, -1,     1);
    } else {
        imagePicker.cameraViewTransform = CGAffineTransformIdentity;
    }
}