It is easy to merge different images to make a single image. It is like pasting images to a canvas and taking picture of that canvas. Below I have explained how to do it.

-(UIImage*)combineImages:(NSMutableArray *)images{

    CGRect frame = self.view.frame;

    CGRect imageViewFrame = CGRectMake(0, 0, frame.size.width/2, frame.size.width/2);

    UIImage *firstImage = [images objectAtIndex:0];
    UIImage *secImage = [images objectAtIndex:1];
    UIImage *imageThree = [images objectAtIndex:2];
    UIImage *imageFour = [images objectAtIndex:3];

    CGSize finalSize = CGSizeMake(frame.size.width, imageViewFrame.size.height*2);

    UIGraphicsBeginImageContextWithOptions(finalSize, YES, 0.0);
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetFillColorWithColor(context, [[UIColor lightGrayColor] CGColor]);
    CGContextFillRect(context, CGRectMake(0, 0, finalSize.width, finalSize.height));

    [firstImage drawInRect:CGRectMake(0, 0, imageViewFrame.size.width, imageViewFrame.size.height)];

    [secImage drawInRect:CGRectMake(imageViewFrame.size.width, 0, imageViewFrame.size.width, imageViewFrame.size.height)];

    [imageThree drawInRect:CGRectMake(0, imageViewFrame.size.height, imageViewFrame.size.width, imageViewFrame.size.height)];

    [imageFour drawInRect:CGRectMake(imageViewFrame.size.width, imageViewFrame.size.height, imageViewFrame.size.width, imageViewFrame.size.height)];

    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;

}

Final result will look like this: