Display large object from database

I am using pgSQL 8.1.4. I have a table that stores pictures, using an oid column.

Now using the SQL functions provided I have successfully saved an image to the table, and managed to export it from the table again.

I am battling to open the image for reading into a stream.  The mentioned functions support opening for exporting a file in SQL are

SELECT lo_export(image.raster, '/tmp/motd') FROM image

    WHERE name = 'beautiful image';



But how do I open a stream for reading? 

inv_fd = lo_open(conn, inv_oid, INV_READ|INV_WRITE);

I have tried to convert this into a SQL statement but INV_READ is not seen as an accepted parameter.