@vaiiav

you can replace the fontawesome icon with css "background"

Example i replace your half-star here in the forum with garfield 😉 

Video = https://www.screencast.com/t/zeXVcZlDw8

search for the code with the browser inspector
you will find this

.fa-star-half::before {
content: "\f089";
}

the replace code looks like

.fa-star-half::before {
content: "";
background: url(/wp-content/uploads/wpforo/avatars/garfield_4.jpg);
background-size: 30px;
background-repeat: no-repeat;
width: 30px;
height: 30px;
left: 0;
position: absolute;
margin-top: -20px; 
margin-left: 35px;
}

add your code to custom css

Dashboard > Forums > Settings > Style (custom css)