wget can't download - 404 error

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»

I had the same problem with a Google Docs URL. Enclosing the URL in quotes did the trick for me:

wget "https://docs.google.com/spreadsheets/export?format=tsv&id=1sSi9f6m-zKteoXA4r4Yq-zfdmL4rjlZRt38mejpdhC23" -O sheet.tsv

You will also get a 404 error if you are using ipv6 and the server only accepts ipv4.

To use ipv4, make a request adding -4:

wget -4 http://www.php.net/get/php-5.4.13.tar.gz/from/this/mirror