Display a random image in the sidebar
Random Image generator for the sidebar
This module comes with the core G3 distribution.
Activate the module: Login -> Admin -> Modules. Check the box next to the module. Click update at the bottom of the page.
Admin -> Appearance -> Manage sidebar. Verify that the imageblock is moved from the 'Available blocks' to 'Active blocks' and in the order you desire with other blocks.
After Version 3.0.1 you can increase the number of images shown. Just change the quantity in the advanced settings.