Large objects - SOS

Hi,
I need to create a large object - a photograph and work with it. I would be
using ODBC (application on Windows NT , db server on Linux)
The doc at
http://gborg.postgresql.org/project/psqlodbc/faq/faq.php?faq_id=52
suggests creating a custom type like this.
create type lo (
   internallength=4,
   externallength=10,
   input=int4in,
   output=int4out,
   default='',
   passedbyvalue
);

I need to define the input & output functions (int4in and int4out).
Can someone give me a clue as to how these functions should be defined?
Some sample code would really help me.

Regards,
Manoj