How to get the different renditions of thumbnail image of author ?

Hi ,

Can anyone has idea on how to get the different renditions available of thumbnail image of author .

I am using the default thumbnail image of author by following link

http://community.lithium.com/restapi/vc/users/id/41110/profiles/avatar

But using this i am getting one author image as in one rendition and another author image in different rendition. I need thumbnail image of all authors in single rendition.

if any one has idea on this can you help me on this