Full ViewController code for http://stackoverflow.com/questions/20494660/uiimage-how-to-resize-bubble-image-with-capinsets/20494861

gistfile1.m

#import "ViewController.h"

// "Change size" button const
#define BUTTON_WIDTH 120
#define BUTTON_HEIGHT 40

#define IMAGE_CAP_INSET_TOP 30.0
#define IMAGE_CAP_INSET_LEFT 30.0
#define IMAGE_CAP_INSET_BOTTOM 30.0
#define IMAGE_CAP_INSET_RIGHT 30.0

@interface ViewController ()

@property (strong, nonatomic) UIImageView *ballonImageView;

@end

@implementation ViewController

- (void)viewDidLoad
{
  [super viewDidLoad];
	// Do any additional setup after loading the view, typically from a nib.
}

- (void)viewWillAppear:(BOOL)animated{
  
//  Create button
  UIButton *changeSizeButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
  [changeSizeButton setFrame:CGRectMake((self.view.frame.size.width - BUTTON_WIDTH)/2, self.view.frame.size.height - BUTTON_HEIGHT, BUTTON_WIDTH, BUTTON_HEIGHT)];
  [changeSizeButton setTitle:@"Change Size" forState:UIControlStateNormal];
  [changeSizeButton addTarget:self action:@selector(changeBallonImageSize) forControlEvents:UIControlEventTouchUpInside];
  
//  Create imageViewForBallon
  _ballonImageView = [[UIImageView alloc] initWithFrame:[self randomRect]];
  UIImage* balloonImage = [self balloonImageWithRect:_ballonImageView.frame];
  [_ballonImageView setImage:balloonImage];

  [self.view addSubview:changeSizeButton];
  [self.view addSubview:_ballonImageView];
}

- (UIImage *)balloonImageWithRect:(CGRect)rect{
  //cap corners
  UIImage *ballonImage = [[UIImage imageNamed:@"balloon"] resizableImageWithCapInsets:UIEdgeInsetsMake(IMAGE_CAP_INSET_TOP, IMAGE_CAP_INSET_LEFT, IMAGE_CAP_INSET_BOTTOM, IMAGE_CAP_INSET_RIGHT) resizingMode:UIImageResizingModeStretch];
  UIImage *arrowImage = [UIImage imageNamed:@"arrow"];
  
  //drawing area
  CGSize newSize = rect.size;
  UIGraphicsBeginImageContext(newSize);
  
  //leave some space for arrow at the bottom
  [ballonImage drawInRect:CGRectMake(0, 0, newSize.width, newSize.height - arrowImage.size.height)];
  //draw arrow at the bottom
  [arrowImage drawInRect:CGRectMake((newSize.width - arrowImage.size.width)/2, newSize.height - arrowImage.size.height, arrowImage.size.width, arrowImage.size.height)];
  
  UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
  
  return newImage;
}

- (void) changeBallonImageSize {
  [_ballonImageView setFrame:[self randomRect]];
  UIImage *newImage = [self balloonImageWithRect:_ballonImageView.frame];
  [_ballonImageView setImage:newImage];
}

// ugly code for random rect :(
// sometemes causes exeption when return rect with 0 width or height
- (CGRect) randomRect {
//  actually it's random in proper bounds
  CGPoint leftTop = [self randomPointInRect:CGRectMake(10, 20, self.view.frame.size.width - 120, self.view.frame.size.height - 120)];
  CGPoint rightBot = [self randomPointInRect:CGRectMake(leftTop.x + 100, leftTop.y + 100, self.view.frame.size.width - leftTop.x - 110, self.view.frame.size.height - leftTop.y - 110)];
  
//  create rect with this two points
  return CGRectMake(leftTop.x, leftTop.y, rightBot.x - leftTop.x, rightBot.y - leftTop.y);
}

- (CGPoint)randomPointInRect:(CGRect)r
{
  CGPoint p = r.origin;
  
  p.x += arc4random_uniform(r.size.width);
  p.y += arc4random_uniform(r.size.height);
  
  return p;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

- (void)dealloc{
  _ballonImageView = nil;
}

@end