ColaIan You can use custom images by using custom icon names, e.g. setting a reaction's icon to custom <reaction name> and then using CSS to style .fa-custom.<reaction name>:before.
Example: custom custom-<image name> (untested code follows)
.fa-custom {
&:before {
display: inline-block;
width: 20px;
height: 20px;
content: "";
margin-right: 0;
background-size: 100% !important;
background: no-repeat 0 0;
}
&.custom-<image name>:before {
background-image: url(<image url>);
}
