This code run from console will generate and execute random codes, whenever it finds something new it stops (just reexecute it and it will continue searching)

  var seen = seen || [];
  while (true) {
    c='';
    m=30*Math.random();
    var a='x0123456789dcp+*~!yPsqa-/^';
    for (var i=0; i<m; i++) {    
      c+=a.charAt(Math.floor(Math.random()*a.length));
    }
    code.value = c;
    buttonClick();
    d=f.getImageData();
    sum=0; 
    for (var i=0; i<5000; i++) { 
      sum+=d.data[i];
    }
    console.log('seen ', sum);
    if (seen.indexOf(sum) < 0) {
      seen.push(sum);
      break;
    }
  } 

Few examples generated by this:

    s*23-yxxx+-7x7s/y-^3sp*
    9sx2+ysx-7ysp+*+
    -P+p*syq6^xp15x/syxyyc-p**