You need to add the referer field in the headers of the HTTP request. With wget, you just need the --header arg :
wget http://www.icerts.com/images/logo.jpg --header "Referer: www.icerts.com"
And the result :
--2011-10-02 02:00:18-- http://www.icerts.com/images/logo.jpg
Résolution de www.icerts.com (www.icerts.com)... 97.74.86.3
Connexion vers www.icerts.com (www.icerts.com)|97.74.86.3|:80...connecté.
requête HTTP transmise, en attente de la réponse...200 OK
Longueur: 6102 (6,0K) [image/jpeg]
Sauvegarde en : «logo.jpg»