If you happen to extract their JS file and locate line #472, you will find that when the 'btn_numbers' property is true, numeric numbers are used; however, if it's false, they get converted to '●', resembling a small black circle. To utilize images for numbers instead, generate an image for every number and insert an
img_name = parseInt(i+1)+".jpg";
<img src=img_name+".jpg">
in place of the numerical counter. Although the code snippet above may not work immediately, it serves as a foundation. Given that the entire code operates within a loop, it will fetch an image corresponding to each created number.