Problem when trying to display image from database

[eluser]FabD[/eluser]
when i put the url

Code:

http://localhost/gerico/index.php/signal/marches/displayimage/1

into the browser I get an error :

Code:

A PHP Error was encountered

Severity: Notice

Message: Undefined variable: Id

Filename: signal/marches.php

Line Number: 74

( ! ) Fatal error: Call to a member function num_rows() on a non-object in C:\WebLocal\Gerico\system\application\models\mmarches.php on line 68
Call Stack
#    Time    Memory    Function    Location
1    0.0023    64544    {main}( )    ..\index.php:0
2    0.0068    115040    require_once( 'C:\WebLocal\Gerico\system\codeigniter\CodeIgniter.php' )    ..\index.php:115
3    0.5081    3393240    call_user_func_array ( )    ..\CodeIgniter.php:232
4    0.5081    3393240    Marches->displayimage( )    ..\CodeIgniter.php:0
5    0.5126    3425264    MMarches->getImage( )    ..\marches.php:74

As concerns the database (Oracle), I have put a jpeg image into the record with id 1
using PL-SQL Developer.