So basically, what's supposed to happen is that it starts out with a photograph of a face, and when you press a number on the keyboard (from 1-6), a piece of the face will be replaced by another persons face. So basically all I need to know is how to get the images that are right now called "1/1.jpg" "2/1.jpg" etc, to select a random image from the specified folder. The folders are just labeled 1 - 6, and I can give the pictures different names if necessary. Yeah, so here's the code I have right now: 

2. PImage face;
3. PImage a;
4. PImage b;
5. PImage c;
6. PImage d;
7. PImage e;
8. PImage f;
9. 
   
10. 
    
11. void setup() {
12.   size (1280, 800);
13.   face = loadImage("background.jpg");
14.   background(face);
15. }
16. 
    
17. void draw(){
18. 
    
19.   
20.   if(key=='1'){
21.     a = loadImage("1/1.jpg");
22.     image(a,0,0);
23.     
24.   }
25.   
26.    
27.   if(key=='2'){
28.     b = loadImage("2/1.jpg");
29.     image(b,640,0);
30.     
31.   }
32.   
33.    
34.   if(key=='3'){
35.     c = loadImage("3/1.jpg");
36.     image(c,0,266);
37.     
38.   }
39.   
40.    
41.   if(key=='4'){
42.     d = loadImage("4/1.jpg");
43.     image(d,640,266);
44.     
45.   }
46.   
47.    
48.   if(key=='5'){
49.     e = loadImage("5/1.jpg");
50.     image(e,0,532);
51.     
52.   }
53.   
54.    
55.   if(key=='6'){
56.     f = loadImage("6/1.jpg");
57.     image(f,640,532);
58.     
59.   }
60.   
61. }

So yeah, how would I make the images random?