Must have package that should be installed by default (if you use Nautilus) :

• nautilus-image-converter

And another file manager (IMHO better than Nautilus) :

• thunar : for example, you can with a simple right click send files or even directory to thunderbird (strictly impossible with Nautilus), you can launch a term in the current directory, you can paste into the folder trackbar, etc.

How to replace definitely Nautilus by Thunar ? 2 solutions :

• http://www.imaginux.com/roadtolinux/dotclear/index.php?2006/10/24/167-thunar-for-gnome
• http://www.lineheight.net/blog/aprire-percorsi-con-thunar-da-gnome