Something goes wrong and i can't edit my post.
Anyway, if i load the jpg as loadStrings and then write it to a file then the characters are differen't, how can i solve this problem?

1. java.io.FilenameFilter jpgFilter = new java.io.FilenameFilter() {
     boolean accept(File dir, String name) {
       return name.toLowerCase().endsWith(".jpg");
     }
   };
   
   String[] filenames;
   
   PrintWriter output;
   
   void setup() {
     size(1024, 768);
     // we'll have a look in the data folder
     java.io.File folder = new java.io.File(dataPath(""));
   
     // let's set a filter (which returns true if file's extension is .jpg)
   
     // list the files in the data folder, passing the filter as parameter
     filenames = folder.list(jpgFilter);
   
     // get and display the number of jpg files
     println(filenames.length + " jpg files in specified directory");
   
     // display the filenames
     for (int i = 0; i < filenames.length; i++) {
       println(filenames[i]);
     }
    
    
   }
   
   void draw(){
     output = createWriter("test1.jpg");
    
     String source = getSource();
     String[] huzzle = getHuzzle();
    
     String[] lines = loadStrings(source);
    
     println("source: "+source);
    
     for(int i = 0; i < lines.length; i++){
       output.println(lines[i]); 
     }
    
    
     output.flush();
     output.close();
   
     noLoop();
    
   }
   
   
   // . . . . . . . .  .
   
   
   String getSource(){
     int r = int(random(0, filenames.length));
     return(filenames[r]);
   }
   
   
   // . . . . . . . .  .
   
   
   String[] getHuzzle(){
     int r = int(random(1, filenames.length));
     String[] huzzle = new String[r];
     for(int i = 0; i < r; i++){
        int r2 = int(random(0, filenames.length));
        huzzle[i] = filenames[r2];
     }
     return huzzle;
   }
   
   

I don't understand what you are trying to do, but reading a binary file like a text is a good recipe to get corrupted, unreadable files.

I want certain parts from a jpg file to be copyd and pasted in another jpg file.
Would loadBytes and saveBytes avoid corrupting it?

As far as I understood you are trying to make a remix with images.
If so, your approach is wrong, a jpg image has compressed data so that you will not be able to load it and manipulate it like a string.
You should load the image in a proper way to processing

PImage b;
// Images must be in the "data" directory to load correctly
b = loadImage("laDefense.jpg");

then paste parts of it into the new image with image command
image(b, 0, 0);

I want to glitch the image.
If i copy and paste some lines within this images



then it becomes this:



(it even looks different in my browser :) )

So that's why i don't use loadImage.

(so loadBytes must work right?)

Yes, loadBytes is probably the way to go. Still probably messing your files, because randomly changing bytes in compressed data might lead to crash the application loading the image, but feel free to experiment...

If i use noLoop it never throws a error (exept corrupt jpeg data but that doesnt matter).
In draw it suddenly get's problems with the temp files again, i have no clue how to fix.

(there need to be a few images in the data directory (jpg afcorse))

1. java.io.FilenameFilter jpgFilter = new java.io.FilenameFilter() {
     boolean accept(File dir, String name) {
       return name.toLowerCase().endsWith(".jpg");
     }
   };
2. String[] filenames;
3. PImage img;
4. 
   void setup() {
     size(800, 600);
5.   java.io.File folder = new java.io.File(dataPath(""));
     filenames = folder.list(jpgFilter);
6.   println(filenames.length + " jpg files in specified directory");
7.   for (int i = 0; i < filenames.length; i++) {
       println(filenames[i]);
     }
     imageMode(CENTER);
   }
8. 
   // . . . . . . . . . .
9. 
   void draw(){
     background(255);
     frameRate(1);
     String source = getSource();
     String[] huzzle = getHuzzle();
    
     byte b[] = loadBytes(source);
    
     for(int i = 2000; i < 2100; i++){
       b[i] = b[i-100];
     }
     deleteFile("huzzled2.jpg");
     saveBytes("huzzled2.jpg", b);
     img = loadImage("../huzzled2.jpg");
     image2(img, width/2, height/2);
     //image(img, 0, 0);
10.   //noLoop();
      //exit();
     
    }
11. 
    // . . . . . . . . . .
12. // this code must change if the format of the sketch will be standing
    void image2(PImage img, int x, int y){
      int w, h;
     
      if(img.width > img.height){
         w = width;
         h = width/img.width * img.height;
      }
      else if(img.width < img.height){
        h = height;
        w = height/img.height * img.width;
      }
      else { // square image
        h = height;
        w = height/img.height * img.width;
      }
      image(img, x, y, w, h);
    }
13. 
    // . . . . . . . . . .
14. 
    void deleteFile(String theFile){
      File dataFile = sketchFile(theFile);
      println(dataFile.getAbsolutePath());
      if(dataFile.exists()){
        dataFile.delete();
      } else {
        println("file to delete not found"); 
      }
    }
15. 
    // . . . . . . . . . .
16. 
    // the image to glitch
    String getSource(){
      int r = int(random(0, filenames.length));
      return(filenames[r]);
    }
17. 
    // . . . . . . . . . .
18. 
    // gives the name of 1 or more images
    String[] getHuzzle(){
      int r = int(random(1, filenames.length));
      String[] huzzle = new String[r];
      for(int i = 0; i < r; i++){
         int r2 = int(random(0, filenames.length));
         huzzle[i] = filenames[r2];
      }
      return huzzle;
    }