main.m

@interface Camera : NSObject

@property (nonatomic, strong) AVCaptureStillImageOutput* stillImageOutput;
@property (nonatomic,strong) AVCaptureSession *session;

- (AVCaptureDevice *)frontFacingCameraIfAvailable;
- (void)setupCaptureSession;
- (void)captureWithBlock:(void(^)(UIImage* block))block;

@end

@implementation Camera

- (AVCaptureDevice *)frontFacingCameraIfAvailable
{
    NSArray *videoDevices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    AVCaptureDevice *captureDevice = nil;
    
    for (AVCaptureDevice *device in videoDevices){
        
        if (device.position == AVCaptureDevicePositionFront){
            
            captureDevice = device;
            break;
        }
    }
    
    //  couldn't find one on the front, so just get the default video device.
    if (!captureDevice){
        
        captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    }
    
    return captureDevice;
}

- (void)setupCaptureSession
{
    self.session = [[AVCaptureSession alloc] init];
    self.session.sessionPreset = AVCaptureSessionPresetMedium;
    
    NSError *error = nil;
    AVCaptureDevice *device = [self frontFacingCameraIfAvailable];
    AVCaptureDeviceInput *input = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
    if (!input) {
        // Handle the error appropriately.
        NSLog(@"ERROR: trying to open camera: %@", error);
    }
    [self.session addInput:input];
    
    self.stillImageOutput = [[AVCaptureStillImageOutput alloc] init];
    NSDictionary *outputSettings = [[NSDictionary alloc] initWithObjectsAndKeys: AVVideoCodecJPEG, AVVideoCodecKey, nil];
    [self.stillImageOutput setOutputSettings:outputSettings];
    
    [self.session addOutput:self.stillImageOutput];
    [self.session startRunning];
}

- (void)captureWithBlock:(void(^)(UIImage* image))block
{
    AVCaptureConnection* videoConnection = nil;
	for (AVCaptureConnection* connection in self.stillImageOutput.connections)
	{
		for (AVCaptureInputPort* port in [connection inputPorts])
		{
			if ([[port mediaType] isEqual:AVMediaTypeVideo])
			{
				videoConnection = connection;
				break;
			}
		}
        
		if (videoConnection)
        {
            break;
        }
	}
    
    NSLog(@"videoConnection = %@",videoConnection);
    NSLog(@"about to request a capture from: %@", self.stillImageOutput);
    
    [self.stillImageOutput captureStillImageAsynchronouslyFromConnection:videoConnection completionHandler: ^(CMSampleBufferRef imageSampleBuffer, NSError *error)
     {
         NSData* imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageSampleBuffer];
         UIImage* image = [[UIImage alloc] initWithData:imageData];
         //NSLog(@"image captured: %@", [imageData bytes]);
         block(image);
     }];
}
@end

int main(int argc, char * argv[])
{
    Camera* camera = [[Camera alloc] init];
    [camera setupCaptureSession];
    
    __block BOOL done = NO;
    
    [camera captureWithBlock:^(UIImage *image)
     {
         done = YES;
     }];
    
    while (!done)
    {
        [[NSRunLoop mainRunLoop] runUntilDate:[NSDate dateWithTimeIntervalSinceNow:0.1]];
    }
    
    return 0;
}