Ok I tested it. Works well via the shell:

Code: 
hyperz@ubuntu:~$ wget http://im4ge.info/files/Im4ge-dt.exe
--2009-10-24 22:02:10--  http://im4ge.info/files/Im4ge-dt.exe
Resolving im4ge.info... 217.23.6.177
Connecting to im4ge.info|217.23.6.177|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 192000 (188K) [application/x-msdos-program]
Saving to: `Im4ge-dt.exe'

100%[======================================>] 192,000      457K/s   in 0.4s    

2009-10-24 22:02:10 (457 KB/s) - `Im4ge-dt.exe' saved [192000/192000]

hyperz@ubuntu:~$ mono Im4ge-dt.exe "Shiretoko_wallpaper.png" 
hyperz@ubuntu:~$
That nicely opened a new tab in firefox to http://im4ge.info/index.php?&showlin...session=jagmvu

It added a Upload Image menu item under scrips to but it doesn't work (just does nothing here).

OS: Ubuntu 9.04 (2.6.28-16-generic kernel)
Gnome: 2.26.1 (Ubuntu 2009-05-06)
Mono:

Code: 
hyperz@ubuntu:~$ mono --version
Mono JIT compiler version 2.4.2.3 (Debian 2.4.2.3+dfsg-2~dhx1~jaunty1)
Copyright (C) 2002-2008 Novell, Inc and Contributors. www.mono-project.com
    TLS:           __thread
    GC:            Included Boehm (with typed GC)
    SIGSEGV:       altstack
    Notifications: epoll
    Architecture:  amd64
    Disabled:      none