jQuery selector img[alt="projects4"] doesn't always work

jQuery selector img[alt="projects4"] doesn't always work

Here is my client's site:
I try ti target the images in the carousel bellow the slider(with 10 images)
Problem is that some work while others don't
Her is a typical snippet that I use:

$('img[alt="projects4"]').on('click',function(){
   jQuery('#extra-text').modal({
  fadeDuration: 1000,
  fadeDelay: 0.50
});
});

Any idea?
Thx