The default logo is located in:
/var/lib/tomcat6/webapps/Oscar12_1/images/OSCAR-LOGO.gif
You can specify an altername logo in the Oscar.properties file:
sudo nano /usr/share/tomcat6/Oscar12_1.properties
loginlogo=
The location of the file is relative to the /var/lib/tomcat6/webapps/Oscar12_1/ directory
If you want to put the replacement image in the images folder, you need to specify that.
loginlogo=images/NEW-LOGO.gif
Note: Any change to the .properties file requires that you restart tomcat
sudo service tomcat6 restart
Once you have changed the .properties file, you can modify the images as required.
Images notes:
600 to 700 pixels high is a good size.
é is Alt-0233