Why google index this ?
In this webpage:

http://www.alvolante.it/news/pompe_benzina_%E2%80%9Ctruccate%E2%80%9D_autostrada-308391044

there is this image:

http://immagini.alvolante.it/sites/default/files/imagecache/anteprima_100/images/rifornimento_benzina.jpg

Why this image is indexed if in the robots.txt there is "Disallow: /sites/" ??

You can see that is indexed from this search:

http://www.google.it/images?q=rifornimento+benzina&um=1&ie=UTF-8&source=og&sa=N&hl=it&tab=wi&biw=1280&bih=712
Why google index this ?
===

In this webpage:

http://www.alvolante.it/news/pompe_benzina_%E2%80%9Ctruccate%E2%80%9D_autostrada-308391044

there is this image:

http://immagini.alvolante.it/sites/default/files/imagecache/anteprima_100/images/rifornimento_benzina.jpg

Why this image is indexed if in the robots.txt there is "Disallow: /sites/" ??

You can see that is indexed from this search:

http://www.google.it/images?q=rifornimento+benzina&um=1&ie=UTF-8&source=og&sa=N&hl=it&tab=wi&biw=1280&bih=712