How to replace a certain ROI with another image?

edit

Thanks for the quick reply Steven but I think that's what I have been doing.

 Mat capturedImage = Highgui.imread(<path/to/captured/image>)
 Mat selectedArea = capturedImage.submat(mDetectedFace) //mDetectedFace is a Rect object
 Mat replaceImage = Highgui.imread(<path/to/replacement/image>)

 replaceImage.copyTo(selectedArea);
 Highgui.imwrite(<path/to/save/directory>, capturedImage)

But nothing happens. The picture is as it is. The replacement image was not copied to the selected area.

First thing, I added your code to your original post. Please do this also if you make changes. You can format code much better in a main post.

You are still using my suggestions wrong. Please try this code, which should do what you want.

   replaceImage.copyTo( capturedImage( mDetectedFace ) );

You cannot create a ROI first than copy to that only. It won't work that way since you just shifting points, but not copying the data. My new suggestion should work. So you can than remove the selectedArea matrix.

Thanks for the posting advice. This may sound pretty stubborn of me but wouldn't your code snippet above be the same as

 replaceImage.copyTo( capturedImage.submat( mDetectedFace ) );

I'm saying this because in Java I can't do

 capturedImage( mDetectedFace );

By the way, how do I insert preformatted code snippets in a comment? Sorry if this fact should be a dead give a way already.

Adding code into a comment is making sure you have a blank line before and after, then position each rule about 5 spaces in front of it. This should do the trick, but again, comments not really for code blocking. I am not familiar with the Java OpenCV implementation, neighter with the function submat. But probably the submat function does call internally the code i did present. Basically Java openCV is created out of openCV wrappers. If a function is not available, create a pull request and try to create a personal wrapper for it?