I setup my forum with custom ranks based on post count, but instead of ranks they are Levels. The first image is the Usergroup image, the image at the bottom is the user Rank Level. I custom coded my postbit legacy just for my forum though, so that feature its not in vBulletin by default. But if you need help with the code, I could help you. Just let me know.
In your case you could change the levels with your own images.
I am not sure what you mean by you don't want the ranks to be based on Post Count. How do you want them to work or increase in rank? If you just want only a few people in a usergroup to have a specific rank/badge image, I think the only way to do that is to edit the users rank yourself via AdminCP. As far as I know anyway, but I could be wrong.
Thank you for your kind offer but MarkFL was able to write an extension that I have been able to use to meet our needs.
To better explain to you what was going on is that with the change from phpBB to vBulletin planned for June an introduction of a two tiered membership system is being imposed:
Community Members - Ranked by post count; this is your traditional user
Fleet Members - this is the higher tier membership and its ranking is not based on post count but on earning your way up a ranking chain through actions they take within the community and other aspects that we participate in. We look at how people contributed over the course of a month and then make decisions on where they are to be placed; there are several echelons as well which is where the "wings" came in; a tradition held up since 2002.
vBulletin didn't have the function built in to accommodate something we had been doing since 2002 but Mark was able to build an extension to accommodate this which I later modified into two so that the Wings for each echelon displayed below the user title while the rank displayed above.
Community Members on the other hand will use the built in vBulletin ranking system because their rank is built in post count as part of the community.