1. PImage[] images;
2. int counter;
3. int lastTime;
4. final int DISPLAY_TIME = 15000;
5. void setup(){
6.   size(500, 500);
7.   images = new PImage[20];
8.   counter = 0;
9.   for (int i = 0; i < images.length; i++) {
10.     images[i] = loadImage("img" + nf(i+1, 2) + ".png");
11.   }
12.   lastTime = millis();
13. }
14. void draw() {
15.   background(255);
16.   fill(00, 64, 128);
17.   text(frameCount, 10, 20);
18.   if (millis() - lastTime >= DISPLAY_TIME) {
19.     counter++;
20.     counter%=images.length;
21.     lastTime = millis();
22.   }
23.   image(images[counter], 50, 50);
24. }

loadImage("img" + nf(i+1, 2) + ".png");

1. counter = random(0,images.length);

would be possible to do random in a different way? would be possible to do a random where the slideshow does not repeat the pictures?

1. int p1, p2;
2. for(int i = 0; i < 1000; i++){
3.   p1 = (int) random(0,images.length);
4.   p2 = (int) random(0,images.length);
5.   PImage temp = images[p1];
6.   images[p1] = images[p2];
7.   images[p2] = p2 = temp;
8. }

1. PImage[] images = new PImage[6]; // put 60 or whatever
2.  
3. void setup()
4. {
5.   for (int i = 0; i < images.length; i++)
6.   {
7.     images[i] = createImage(5, 5, RGB); // Just for demo purpose
8.   }
9.   println(images);
10.   // Put the images in an array list as Java can shuffle
11.   // such object, not arrays (sic).
12.   ArrayList<PImage> imagesToMix = new ArrayList<PImage>();
13.   Collections.addAll(imagesToMix, images);
14.   Collections.shuffle(imagesToMix);
15.   imagesToMix.toArray(images);
16.   println(images);
17.  
18.   exit();
19. }

1.   for (int i = images.length - 1; i > 0; i--)
2.   {
3.     int j = int(random(i + 1));
4.     // Swap
5.     PImage t = images[i];
6.     images[i] = images[j];
7.     images[j] = t;
8.   }

1.     counter++;
2.     counter%=images.length;

1. PrintWriter output;

this in setup() 

1. // Create a new file in the sketch directory
   
2. output = createWriter("positions.txt");

1. void draw()
2. {
3.   background(255);
4.   fill(#005599);
5.   text(frameCount, 10, 20); // Shows the sketch isn't stopped between each image
6.  
7.   if (millis() - lastTime >= DISPLAY_TIME) // Time to display next image
8.   {
9.     // Increment counter, then compute its modulo, ie. reset it at zero when reaching images.length
10.    
11.     // counter stuff etc.
12.     lastTime = millis();
13.  
14.   }
15.   image(images[counter], 0,0);
16.  
17.   println(images[counter]);

18.  output.println(images[counter]); // Write the name to the file

19. 
    
20. }

and of course 

1. void keyPressed() {
   
2. output.flush(); // Writes the remaining data to the file
   
3. output.close(); // Finishes the file
   
4. exit(); // Stops the program
   
5. }

1. // loadStrings(var)         //Because for every day i'll have a different txt file.
2. void setup() {
3.   size (300, 300);
4.   // PFont metaBold;
5.   // metaBold = createFont("fonts/Meta-Bold.vlw.gz", 44);
6.   //setFont(metaBold);
7.   // noLoop();
8. }
9. void draw() {
10.   background(0);
11.   int d = day();    // Values from 1 - 31
12.   int m = month();  // Values from 1 - 12
13.   int y = year();   // 2003, 2004, 2005, etc.
14.   String strDay = nf(d, 2);
15.   text( "Day " + strDay, 10, 28);
16.   String strMon = nf(m, 2);
17.   text("month " + strMon, 10, 56);
18.   String strYear = str(y);
19.   text("year " + strYear, 10, 84);
20.   //
21.   String myFilename= strYear+strMon+strDay+".txt";
22.   //
23.   text("File: "+myFilename, 10, 116);
24.   // loadSomething(myFilename);
25. }
26. void loadSomething(String name1) {
27.   String lines[] = loadStrings(name1);
28.   println("there are "
29.     + lines.length
30.     + " lines");
31.   for (int i=0; i < lines.length; i++) {
32.     println(lines[i]);
33.   }
34. }

import java.io.*;
import java.util.Date;
import java.text.DateFormat;
import java.text.SimpleDateFormat;

private PrintWriter output;
private OutputStream os;
private DateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); // Ansi date format

int counter; // Automatically initialized at 0
final int DISPLAY_TIME = 5000; // 5000 ms = 5 seconds
int lastTime; // When the current image was first displayed

String logFileName = "FileList.txt";

/* First version, taking the images from the data folder
final int IMAGE_NB = 20; // Supposing we have 20 images
File[] files = new File[IMAGE_NB];
PImage[] images = new PImage[IMAGE_NB];

void setup()
{
  size(700, 700);

  for (int i = 0; i < IMAGE_NB; i++)
  {
    files[i] = dataFile("img" + nf(i+1, 2) + ".png"); // nf() allows to generate 01, 02, etc.
    images[i] = loadImage(files[i].getAbsolutePath());
  }
  randomizeImages();
  lastTime = millis();
}
*/

String imageFolderPath = "G:/Images";
File[] files;
PImage[] images;

// Second version, just listing the images
void setup()
{
  size(700, 700);

  File imageFolder = new File(imageFolderPath);
  files = imageFolder.listFiles(new FileFilter()
  {
    public boolean accept(File file)
    {
      if (file.isDirectory())
        return false; // Only files. A directory can have a dot in its name...
      String name = file.getName();
      return name.endsWith(".jpg") || name.endsWith(".png") || name.endsWith(".gif");
    }
  });
  images = new PImage[files.length];

  for (int i = 0; i < files.length; i++)
  {
    images[i] = loadImage(files[i].getAbsolutePath());
  }
  randomizeImages();
  showImageInfo();
  lastTime = millis();
}

void draw()
{
  background(255);
  fill(#005599);

  if (millis() - lastTime >= DISPLAY_TIME) // Time to display next image
  {
    counter++;
    if (counter == files.length) // Or IMAGE_NB
    {
      // Displayed all images, re-randomize the images
      randomizeImages();
    }
    lastTime = millis();
    showImageInfo();
  }
  image(images[counter], 0,0);
}

void randomizeImages()
{
  for (int i = images.length - 1; i > 0; i--)
  {
    int j = int(random(i + 1));
    // Swap
    PImage ti = images[i];
    images[i] = images[j];
    images[j] = ti;
    // Swap
    File tf = files[i];
    files[i] = files[j];
    files[j] = tf;
  }
}

void showImageInfo()
{
  File f = files[counter];
  trace("Name: " + f.getName());
  trace("Size: " + f.length());
  String lastModified = dateFormat.format(new Date(f.lastModified()));
  trace("Last Modified: " + lastModified);
  trace("-----------------------");
}

void trace(String line)
{
  println(line);
  log(line);
}

/*-- A simple logger --*/

public void log(String line)
{
  // The file is opened on each write, in append mode
  PrintWriter output = null;
  try
  {
    // Create a file writer in append mode
    output = new PrintWriter(new FileWriter(sketchPath(logFileName), true));
    output.println(line);
  }
  catch (IOException e)
  {
    e.printStackTrace(); // Dumb and primitive exception handling...
    output = null;
  }
  finally
  {
    if (output != null)
    {
      output.close();
    }
  }
}

String imageFolderPath = "G:/Images";

  for (int i = 0; i < IMAGE_NB; i++)
  {
    files[i] = dataFile("img" + nf(i+1, 2) + ".png"); // nf() allows to generate 01, 02, etc.
    images[i] = loadImage(files[i].getAbsolutePath());
  }

1. files[i] = "img" + nf(i + 1, 2) + ".png";
2. images[i] = loadImage(files[i]);

Make files a String[]