I don't know how you could do this unless you used something like Imagemagick . Doing so would require some serious modifications and lots of new code. You also would have to require all users upload their image to your server (which is a potential security hazard.)
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.