Are you running this from the Processing PDE?

I can't recreate your problem. I have no problem saving in the regular manner.

1. PImage faceTemp;
2. 
   
3. void setup() {
4.   size(320,240);
5.   faceTemp = createImage(320, 240, RGB);
6. }
7. 
   
8. void draw() {
9. }
10. 
    
11. void keyPressed() {
12.   faceTemp.save("face.jpg");
13.   exit();
    
14. }

All right, now I'm starting to see the problem from your first and last post.

With this line you probably replaced the PImage with an opencv type image, which has not the same functionality.

1. faceTemp = opencv.image();

Instead you need to write the image to the PImage (not replace it).

However this is a contributed library (opencv) question now, which I can't really help you with, because I don't use opencv.

But if I had to guess I would say instead of the above line, just use something like this...

1. faceTemp = opencv.image().get();

or maybe this (using creategraphics with begin-enddraw)...

1. image( opencv.image(), 0, 0 );

So again, the problem is not the PImage saving, but the transfer from opencv image to PImage.

Brilliant Clues!