Suggestion for the icons

While i don’t use the plugin, i did noticed some of my clients using it and did have some complaints that the images was looking pixlated on hisres screens like Retina.

However, why don’t use font icons instead? Or as an option. They scale (as they are vectors) is supported almost everywhere and is easy to style. A starter point could be the icomoon webapp and create a custom font using only the relevant icon(s) and add them by @fontface.

Example CSS:

/* Change to whatever class or rel you want */
a[rel="nofollow"]:after {
margin: 0 0 0 4px;
padding: 1px;
content: "\f08e"; /* The icon entity value*/
font: 0.78em "your-iconfont-example";
color: #616262; }

https://www.ads-software.com/extend/plugins/wp-external-links/