Where exactly do you need help?
copying parts of the image can be done with copy()
For example:

1. int offset = 20;
   
   void setup() {
     // load an image
     PImage srcImage = loadImage("image.jpg");
    
     int w = srcImage.width;
     int h = srcImage.height;
   
     // create new image
     PImage img = createImage(w, h, RGB);
    
     // copy parts of the source-image into the new one
     img.copy(srcImage, 0, 0, w, offset, 0, h-offset, w, offset);
     img.copy(srcImage, 0, offset, w, h-offset, 0, 0, w, h-offset);
    
     image(img, 0, 0);
   }

If that is what you had in mind, not sure if i understood your idea correctly.

I must translate the source image (loaded by selectInput) up, down, left and right, by pressing the appropriate keys (U,D,L,R)... excuse me,I have not explained well my problem..

OK, think i know what you want to do, but not where you need help.
To "translate" the picture, you can use copy(), as i wrote above.
To capture the key-events you can use keyPressed().
Would really be a lot easier, if you post the code that you have so far.

i have only this part... how can I insert copy, translate and keypress funciotns?

You need two variables, one for the x coordinate of the image, another for the y coordinate.
You use these variables in the image() call, and you update these values in keyPressed(), as explained.
No need to copy the image, just display it at a different place.

look at that ;) where am I wrong?

Well, you don't follow my advice...

Some remarks:
- You can use if () { } else if () { } else { }
No need to nest the else conditions.
- translate() doesn't take a PImage parameter.
- No need for translate() if you follow my advice.
- You can use character literals: if (key == 'a') (single quote).
- No need for copy() either, as I wrote.
- You should have a draw() method, making the image() call after a background() call.

Thank you! 

This is what you mean?

2. PImage img;
3. PImage selection;
4. int x, y;
5. 
   
6. void setup() {
7.   img= loadImage(selectInput());
8.   size(img.width, img.height);
9.   image(img, 0, 0); 
10. 
    
11. }
12. 
    
13. void draw () {
14. if(keyPressed) {
15.     if (key == 'u' || key == 'U') {
16.       image (img, 0,-20);
17. }
18. }
19. if(keyPressed) {
20.     if (key == 'd' || key == 'D') {
21.       image (img, 0,+20);
22. } 
23. }
24. if(keyPressed) {
25.     if (key == 'l' || key == 'L') {
26.       image (img, -20,0);
27. }
28. }
29. if(keyPressed) {
30.     if (key == 'r' || key == 'R') {
31.       image (img, +20,0);
32.   }   
33.     }
34.     if(keyPressed) {
35.     if (key == 'o' || key == 'O') {
36.       image (img, 0,0);
37.   }   
38.     }
39.     }

I don't know why you dropped the keyPressed() function. BTW, no need to repeat the if (keyPressed) test... But this is better tested in keyPressed() itself (where the boolean isn't necessary).
You created x and y but you don't use them. You should have image(img, x, y) once in draw(), and you should update x and y depending on the pressed key. And you don't call background().

Side note: there is probably an example shipped with Processing showing such behavior. Also in the forum. But it is harder to search because lot of newbies use subjects as poor as your (it is obvious to search help, in the Programming Questions forum, and that's about a sketch: no useful information there).