Main.java

package fr.leroideskiwis.imagedecutting;

import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Main {

    private Scanner scanner = new Scanner(System.in);

    private Main() throws IOException {

        File directory;
        do {

            directory = new File(readString("Chemin du dossier : "));

        }while(!directory.exists() && !directory.isDirectory());

        int sizeX = readInt("Taille des fichiers à l'horizontale : ");
        int sizeY = readInt("Taille des fichiers à la verticale : ");

        int imageX = readInt("Nombre d'images à l'horizontale : ");
        int imageY = readInt("Nombre d'images à la verticale : ");
        BufferedImage finalImage = null;

        for(int x = 0; x < imageX; x++){
            for(int y = 0; y < imageY; y++) {
                try {

                    int index = x*imageX+y;
                    int maxIndex = imageX*imageX+imageY;
                    File file = directory.listFiles()[x*imageX+y];
                    int cursorX = x*sizeX;
                    int cursorY = y*sizeY;

                    BufferedImage image = ImageIO.read(file);
                    if (finalImage == null) finalImage = new BufferedImage(sizeX * imageX, sizeY * imageY, image.getType());

                    for(int x1 = 0; x1 < sizeX; x1++){
                        for(int y1 = 0; y1 < sizeY; y1++){

                            finalImage.setRGB(cursorX+x1, cursorY+y1, image.getRGB(x1,y1));

                        }
                    }

                    System.out.println("Création "+index+"/"+maxIndex+" ("+getPourc(index, maxIndex)+")");

                } catch (Exception exception) {
                }
            }


        }

        finalImage.flush();

        ImageIO.write(finalImage, "png", generateFile(directory.getAbsolutePath()+"/final", ".png"));


    }

    private float getPourc(float i, float i1){

        return (i/i1)*100;

    }

    private File generateFile(String path, String extension){

        File file = new File(path+extension);

        for(int i = 0; file.exists(); i++){
            file = new File(path+i+extension);
        }

        return file;

    }

    private int readInt(String s) {

        String str;

        do {

            str = readString(s);

        }while(!isNumber(str));

        return Integer.parseInt(str);

    }

    private boolean isNumber(String s){
        try{
            Integer.parseInt(s);
            return true;
        }catch(Exception ex){
            return false;
        }
    }

    public static void main(String[] args) throws IOException {
	    new Main();
    }

    private String readString(String string){
        System.out.print(string);
        String readed = scanner.nextLine();
        System.out.println();
        return readed;
    }
}

Avec les textures de minecraft ça donne ça :