The ideal way would be if the module allowed us to insert our own images to the site, but this was requested previously and Closed (won't fix) https://www.drupal.org/node/1895012#comment-10310687
I did however managed to find a workaround for this by inserting my own custom images using CSS, and adding the new images to my theme. I +1 this as a feature request, as hiding the existing images with 'display:none' is certainly not ideal.
You can see a live example of this code in action at http://www.kindconsumer.com in the 'Share' section at the bottom.
`.service-links a {
width: 30px;
height: 30px;
color: #fff;
display: block;
overflow: hidden;
float: left;
padding-right: 5px;
}
.service-links img {
display: none;
}
.service-links-facebook {
background: url(../img/facebook.png) 0 0 no-repeat transparent;
}
.service-links-linkedin {
background: url(../img/linkedin.png) 0 0 no-repeat transparent;
}
.service-links-twitter {
background: url(../img/twitter.png) 0 0 no-repeat transparent;
}`