Resolution requires performance of three tasks.
- Modify Confluence Global stylesheet if global theme is used.
- Modify Confluence Space style sheets if another theme is used.
- Transform rectangular images to square images while maintaining original scaling of L X W. This can be done with GIMP.
Task 1 needs to be done once for the entire system.
Repeat Task 2 and Task 3 for each space having a non-default logo (which is already round).
Here is a copy of the CSS code.