Special:AchievementsCustomize (on your wiki) allows you to upload simple square images without the bronze/gold/silver outline, have them auto-cut and auto-formatted, and turned into badges with the outline, similar to those on every wiki. 99% of badges on wikis with "customized badges" look very similar as a result of the automation of this process. You can also customize the names of the achievements, and add more achievements.
Or with a little more effort, you could make very customized badges like those I made for my wiki, if you're interested. Takes a lot of effort and work with an image program though.