- (UIImage*) maskImage:(UIImage *)image {

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

UIImage *maskImage = [UIImage imageNamed:@"mask.png"];
CGImageRef maskImageRef = [maskImage CGImage];

// create a bitmap graphics context the size of the image
CGContextRef mainViewContentContext = CGBitmapContextCreate (NULL, maskImage.size.width, maskImage.size.height, 8, 0, colorSpace, kCGImageAlphaPremultipliedLast);

if (mainViewContentContext==NULL)
	return NULL;

CGFloat ratio = 0;

ratio = maskImage.size.width/ image.size.width;

if(ratio * image.size.height < maskImage.size.height) {
	ratio = maskImage.size.height/ image.size.height;
} 

CGRect rect1  = {{0, 0}, {maskImage.size.width, maskImage.size.height}};
CGRect rect2  = {{-((image.size.width*ratio)-maskImage.size.width)/2 , -((image.size.height*ratio)-maskImage.size.height)/2}, {image.size.width*ratio, image.size.height*ratio}};

CGContextClipToMask(mainViewContentContext, rect1, maskImageRef);
CGContextDrawImage(mainViewContentContext, rect2, image.CGImage);

// Create CGImageRef of the main view bitmap content, and then
// release that bitmap context
CGImageRef newImage = CGBitmapContextCreateImage(mainViewContentContext);
CGContextRelease(mainViewContentContext);

UIImage *theImage = [UIImage imageWithCGImage:newImage];

CGImageRelease(newImage);

// return the image
return theImage;
}