and, finally:

function setup() {
  var title=document.getElementById('title');
  title.textContent=g_dir;
  get_pic();
}

All being well, your quiz should work just as before.

Much of the foregoing may seem like overkill but I think you'll be impressed by where this is all heading, so bear with me.

Prepare a new quiz (mine is Movies) by finding suitable images and storing them in a Movies directory. Don't delete your other directory of images.

Add to your pics.js file like this:

g_Landmarks=[
'Big Ben',
...
'Taj Mahal'
];
g_Movies=[
'Australia',
'Babe',
'Crocodile Dundee',
'Dead Calm',
'Evil Angels',
'Gallipoli',
'Japanese Story',
'The Piano'
];

Don't forget to rename your new images, 0.jpg ...