Dropdown lists containing images are not possible, i learned the hard way..
I saw it once and wanted to make it and lost HOURS.. then asked the profesionals around here and heard that html does not do images in dropdown lists... what i seen was FLASHchat doing it.. and assumed it would be possible..
On the other hand for you case.. do you actually think it will be possible to have like 50 images with a reasonable thumbnail height in a dropdown ? In my case i wanted to put in 11 pixel high smilies.. Your thumbs will be large and the list will be long..
Instead, CB can do already what you want, i think. How about:
1) Forget about image upload system and its link, disable that.
2) Create a CHECKBOX field called My ID photo.
3) Create a new directory of your choosing and upload those pics you have.
4) Add as many fields as you need and enter <img src=images/IDs/IMAGEFILENAME1.jpg> in each field
Ofcourse you change the directory for your own and change each imagefilename to a new one..
What this will do, i create a selfwrapping list of those images. You will not have big sized versions of them. But you CAN use this field in the user lists like it was the usual avatar field.
I dont think it will be a good solution for a big site but for a small company site it just might do..
Good luck