How can I place an image behind an imageView

I've got an image which contains multiple layers. The user can set a picture as a layer. However when there isn't a picture available I'd like to have a replacement picture.

I think I got two options:

1. check if the image (taken photo) is loaded into my directory. if not开发者_JS百科 place the other image.
2. placing the other image (photo_icon.png) to the back of the UIImageView (image1). When a photo hasn't been taken the image becomes visible.

Here's a snippit of my code so far.

NSString *docDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    NSString *pngFilePath = [NSString stringWithFormat:@"%@/photo1.png",docDir];
    UIImage *img = [[UIImage alloc] initWithContentsOfFile:pngFilePath];
    [image1 setImage:img];
    image1.layer.cornerRadius = 15.0;
    image1.layer.masksToBounds = YES;

    CALayer *sublayer = [CALayer layer];
    image1.layer.borderColor = [UIColor blackColor].CGColor;
    image1.layer.borderWidth = 3.5;
    [image1.layer addSublayer:sublayer];    

    CALayer *imageLayer = [CALayer layer];
    imageLayer.frame = image1.bounds;
    imageLayer.cornerRadius = 10.0;
    imageLayer.contents = (id) [UIImage imageNamed:@"Upperlayer.png"].CGImage;
    imageLayer.masksToBounds = YES;
    [sublayer addSublayer:imageLayer];

replacing the image1 for the image which is needed I use:

    CALayer *imageBackLayer = [CALayer layer];
    imageBackLayer.frame = image1.bounds;
    imageBackLayer.cornerRadius = 10.0;
    imageBackLayer.contents = (id) [UIImage imageNamed:@"photo_icon.png"].CGImage;
    imageBackLayer.masksToBounds = NO;
    [sublayer insertSublayer:imageBackLayer below: image1.layer ];

Thanks in advance!

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you can use opacity for the image to show/hide.