Hope this is fine for the off topic area.

I make banners and graphics for an online art and gaming community, around 900 members now. We wanted to reward the members who invite other artists who actually stay and post, maybe with a custom badge I would design in GIMP.

The problem was the numbers. The default invite counts included everyone who joined and left within a day. We switched to an invite tracker that filters those out, and the list of top inviters changed quite a bit.

Has anyone here designed badges or rank icons for a community? I would love to see what worked for you.

Not those but have you considered making a template and changing Name and any other information you need to (maybe - date joined; rank; etc.)?

What I have done is certificates etc; for lots of people and changing the information as needed.
If you can easily put your member's information in a spreadsheet. You could do those already there from that and then members as they join.

I did this in the microsoft publisher app using gimp for any images I needed but there are other apps similar