Hi,

I'd add a call to setup() in your code.
In which i'd define the size of the sketch window and load all images in memory.
That's a not a good option to redefine the size of the sketch window each draw() cycles.

Another thing, u're reloading all images each time mousePressed();

Then on mousePressed() event, i'd clean the current image (calling background()) and then draw the next image.

I'd suggest to search the forum (a good ability to have), this question was asked tons of time.

anchnk is right, your code should look something like this:

1. int N = 5;
   int Current = 0;
   PImage[] Pics;
   int W, H;
   void Setup_ArrayPic() {
     Pics = new PImage[N];
     for(int i = 0; i < N; i++) {
       Pics[i] = loadImage("T" + (i + 1) +".jpg");   
     }
   }
   void setup(){
      size(800, 800);
      Setup_ArrayPic();
   }
   void draw() {
     image(Pics[Current], 0, 0);
   }
   
   void mousePressed() {
     Current = (Current + 1)%N;
   }