Remove rogue app from menu bar
This is likely a status item, not a menu extra. (Not being able to move it around or remove it by holding ⌘ and dragging is the way to find out.)

In Activity Monitor (in /Applications/Utilities), set the pop-up menu to "My Processes" and look for anything that sounds related to the scanner vendor. Also, check ~/Library/LaunchAgents for a file that mentions the vendor in its name. Lastly, check System Preferences → Accounts → (your account) → Login Items.