mojoBlog Role    CB and Joomla Group   Upload Access 
-------------    -------------------   ------------- 
Contributor      Registered            No 
Author           Registered            No 
Editor           Registered            Yes 
Administrator    Registered            Yes 
Contributor      Super Administrator   No 
Author           Super Administrator   No 
Editor           Super Administrator   Yes 
Administrator    Super Administrator   Yes

So,in a nutshell.. only a mojo-Editor or mojo-Administrator can upload images.